diff --git a/DEPS b/DEPS
index 578d9833e9b..2ebbfbb795c 100644
--- a/DEPS
+++ b/DEPS
@@ -23,7 +23,6 @@ vars = {
 
   # Chromium git
   "chromium_git": "https://chromium.googlesource.com",
-  "fuchsia_git": "https://fuchsia.googlesource.com",
 
   # Only use this temporarily while waiting for a mirror for a new package.
   "github_dartlang": "https://github.com/dart-lang/%s.git",
@@ -31,12 +30,9 @@ vars = {
   "gyp_rev": "@6ee91ad8659871916f9aa840d42e1513befdf638",
   "co19_rev": "@4af9ef149be554216c5bb16cbac8e50d4c28cdf1",
 
-  # Revisions of GN related dependencies. This should match the revision
-  # pulled by Flutter.
-  "buildtools_revision": "@c8db819853bcf8ce1635a8b7a395820f39b5a9fc",
-
-  # Scripts that make 'git cl format' work.
-  "clang_format_scripts_rev": "@c09c8deeac31f05bd801995c475e7c8070f9ecda",
+  # Revisions of GN related dependencies.
+  "buildtools_revision": "@39b1db2ab4aa4b2ccaa263c29bdf63e7c1ee28aa",
+  "clang_format_rev": "@0ed791d1387a3c9146ea6c453c646f3c0fc97784",
 
   "gperftools_revision": "@02eeed29df112728564a5dde6417fa4622b57a06",
 
@@ -136,10 +132,11 @@ deps = {
 
   # Stuff needed for GN build.
   Var("dart_root") + "/buildtools":
-     Var("fuchsia_git") + "/buildtools" + Var("buildtools_revision"),
+     Var('chromium_git') + '/chromium/buildtools.git' +
+     Var('buildtools_revision'),
   Var("dart_root") + "/buildtools/clang_format/script":
     Var("chromium_git") + "/chromium/llvm-project/cfe/tools/clang-format.git" +
-    Var("clang_format_scripts_rev"),
+    Var("clang_format_rev"),
 
   Var("dart_root") + "/tests/co19/src":
       (Var("github_mirror") % "co19") + Var("co19_rev"),
@@ -349,6 +346,11 @@ deps = {
 }
 
 deps_os = {
+  "android": {
+    Var("dart_root") + "/third_party/android_tools":
+      Var("chromium_git") + "/android_tools.git" +
+      "@aaeda3d69df4b4352e3cac7c16bea7f16bd1ec12",
+  },
   "win": {
     Var("dart_root") + "/third_party/cygwin":
       Var("chromium_git") + "/chromium/deps/cygwin.git" +
@@ -359,6 +361,98 @@ deps_os = {
 # TODO(iposva): Move the necessary tools so that hooks can be run
 # without the runtime being available.
 hooks = [
+  # Pull GN binaries. This needs to be before running GYP below.
+  {
+    'name': 'gn_linux64',
+    'pattern': '.',
+    'action': [
+      'download_from_google_storage',
+      '--no_auth',
+      '--no_resume',
+      '--quiet',
+      '--platform=linux*',
+      '--bucket',
+      'chromium-gn',
+      '-s',
+      Var('dart_root') + '/buildtools/linux64/gn.sha1',
+    ],
+  },
+  {
+    'name': 'gn_mac',
+    'pattern': '.',
+    'action': [
+      'download_from_google_storage',
+      '--no_auth',
+      '--no_resume',
+      '--quiet',
+      '--platform=darwin',
+      '--bucket',
+      'chromium-gn',
+      '-s',
+      Var('dart_root') + '/buildtools/mac/gn.sha1',
+    ],
+  },
+  {
+    'name': 'gn_win',
+    'pattern': '.',
+    'action': [
+      'download_from_google_storage',
+      '--no_auth',
+      '--no_resume',
+      '--quiet',
+      '--platform=win*',
+      '--bucket',
+      'chromium-gn',
+      '-s',
+      Var('dart_root') + '/buildtools/win/gn.exe.sha1',
+    ],
+  },
+  # Pull clang-format binaries using checked-in hashes.
+  {
+    'name': 'clang_format_win',
+    'pattern': '.',
+    'action': [
+      'download_from_google_storage',
+      '--no_auth',
+      '--no_resume',
+      '--quiet',
+      '--platform=win32',
+      '--bucket',
+      'chromium-clang-format',
+      '-s',
+      Var('dart_root') + '/buildtools/win/clang-format.exe.sha1',
+    ],
+  },
+  {
+    'name': 'clang_format_linux',
+    'pattern': '.',
+    'action': [
+      'download_from_google_storage',
+      '--no_auth',
+      '--no_resume',
+      '--quiet',
+      '--platform=linux*',
+      '--bucket',
+      'chromium-clang-format',
+      '-s',
+      Var('dart_root') + '/buildtools/linux64/clang-format.sha1',
+    ],
+  },
+  {
+    'name': 'clang_format_mac',
+    'pattern': '.',
+    'action': [
+      'download_from_google_storage',
+      '--no_auth',
+      '--no_resume',
+      '--quiet',
+      '--platform=darwin',
+      '--bucket',
+      'chromium-clang-format',
+      '-s',
+      Var('dart_root') + '/buildtools/mac/clang-format.sha1',
+    ],
+  },
   {
     'name': 'd8_testing_binaries',
     'pattern': '.',
@@ -464,6 +558,21 @@ hooks = [
       Var('dart_root') + "/third_party/gsutil.tar.gz.sha1",
     ],
   },
+  {
+    "name": "clang",
+    "pattern": ".",
+    "action": [
+      "download_from_google_storage",
+      "--no_auth",
+      "--no_resume",
+      "--bucket",
+      "dart-dependencies",
+      "--platform=linux*",
+      "--extract",
+      "-s",
+      Var('dart_root') + "/third_party/clang.tar.gz.sha1",
+    ],
+  },
   {
     # Pull Debian wheezy sysroot for i386 Linux
     'name': 'sysroot_i386',
@@ -479,14 +588,10 @@ hooks = [
                '--running-as-hook', '--arch', 'amd64'],
   },
   {
-    'name': 'download_android_tools',
+    # Pull clang if needed or requested via GYP_DEFINES.
+    'name': 'gn_clang',
     'pattern': '.',
-    'action': ['python', 'sdk/tools/android/download_android_tools.py'],
-  },
-  {
-    'name': 'buildtools',
-    'pattern': '.',
-    'action': ['python', 'sdk/tools/buildtools/update.py'],
+    'action': ['python', 'sdk/tools/clang/scripts/update.py', '--if-needed'],
   },
   {
     # Update the Windows toolchain if necessary.
diff --git a/build/config/android/config.gni b/build/config/android/config.gni
index b8d705fceb5..33469666d33 100644
--- a/build/config/android/config.gni
+++ b/build/config/android/config.gni
@@ -62,11 +62,7 @@ if (is_android) {
 
   # Subdirectories inside android_ndk_root that contain the sysroot for the
   # associated platform.
-  if (current_cpu == "x64" || current_cpu == "arm64") {
-    _android_api_level = 22
-  } else {
-    _android_api_level = 16
-  }
+  _android_api_level = 16
   x86_android_sysroot_subdir =
       "platforms/android-${_android_api_level}/arch-x86"
   arm_android_sysroot_subdir =
@@ -174,5 +170,5 @@ if (is_android) {
     assert(false, "Unknown Android ABI: " + current_cpu)
   }
 
-  android_log_tag = "\"dart\""
+  android_log_tag = "\"flutter\""
 }
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index f495361291f..8c1818b2484 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -130,6 +130,17 @@ config("compiler") {
     cflags_objcc += extra_flags
   }
 
+  if (is_clang) {
+    # This is here so that all files get recompiled after a clang roll and
+    # when turning clang on or off. (defines are passed via the command line,
+    # and build system rebuild things when their commandline changes). Nothing
+    # should ever read this define.
+    defines +=
+        [ "CR_CLANG_REVISION=" + exec_script("//tools/clang/scripts/update.py",
+                                             [ "--print-revision" ],
+                                             "trim string") ]
+  }
+
   # Mac-specific compiler flags setup.
   # ----------------------------------
   if (is_mac) {
@@ -354,8 +365,7 @@ config("compiler") {
     defines += [ "HAVE_SYS_UIO_H" ]
 
     # Use gold for Android for most CPU architectures.
-    if (current_cpu == "x86" || current_cpu == "x64" || current_cpu == "arm" ||
-        current_cpu == "arm64") {
+    if (current_cpu == "x86" || current_cpu == "x64" || current_cpu == "arm") {
       ldflags += [ "-fuse-ld=gold" ]
       if (is_clang) {
         # Let clang find the ld.gold in the NDK.
@@ -365,8 +375,10 @@ config("compiler") {
     }
 
     ldflags += [
-      # Don't re-export visible symbols from libraries.
-      "-Wl,--exclude-libs,ALL",
+      # Don't allow visible symbols from libgcc or libc++ to be
+      # re-exported.
+      "-Wl,--exclude-libs=libgcc.a",
+      "-Wl,--exclude-libs=libc++_static.a",
     ]
     if (current_cpu == "arm") {
       ldflags += [
@@ -379,15 +391,9 @@ config("compiler") {
       if (current_cpu == "arm") {
         cflags += [ "--target=arm-linux-androideabi" ]
         ldflags += [ "--target=arm-linux-androideabi" ]
-      } else if (current_cpu == "arm64") {
-        cflags += [ "--target=aarch64-linux-android" ]
-        ldflags += [ "--target=aarch64-linux-android" ]
       } else if (current_cpu == "x86") {
-        cflags += [ "--target=i686-linux-androideabi" ]
-        ldflags += [ "--target=i686-linux-androideabi" ]
-      } else if (current_cpu == "x64") {
-        cflags += [ "--target=x86_64-linux-androideabi" ]
-        ldflags += [ "--target=x86_64-linux-androideabi" ]
+        cflags += [ "--target=x86-linux-androideabi" ]
+        ldflags += [ "--target=x86-linux-androideabi" ]
       }
     }
   }
@@ -477,19 +483,25 @@ config("runtime_library") {
     ]
 
     lib_dirs += [ "$android_libcpp_root/libs/$android_app_abi" ]
+    libs += [ "$android_libcpp_library" ]
 
-    libs += [
-      "$android_libcpp_library",
-      "c++abi",
-      "android_support",
-    ]
-
-    if (current_cpu == "arm") {
-      libs += [ "unwind" ]
+    if (current_cpu == "mipsel") {
+      libs += [
+        # ld linker is used for mips Android, and ld does not accept library
+        # absolute path prefixed by "-l"; Since libgcc does not exist in mips
+        # sysroot the proper library will be linked.
+        # TODO(gordanac): Remove once gold linker is used for mips Android.
+        "gcc",
+      ]
+    } else {
+      libs += [
+        # Manually link the libgcc.a that the cross compiler uses. This is
+        # absolute because the linker will look inside the sysroot if it's not.
+        rebase_path(android_libgcc_file),
+      ]
     }
 
     libs += [
-      "gcc",
       "c",
       "dl",
       "m",
diff --git a/build/toolchain/android/BUILD.gn b/build/toolchain/android/BUILD.gn
index 90e1256da80..5e4847349d1 100644
--- a/build/toolchain/android/BUILD.gn
+++ b/build/toolchain/android/BUILD.gn
@@ -47,16 +47,7 @@ template("android_gcc_toolchain") {
 
     is_clang = invoker.is_clang
     if (is_clang) {
-      host_suffix = ""
-      if (host_os == "linux") {
-        host_suffix = "x86_64-linux"
-      } else if (host_os == "mac") {
-        host_suffix = "x86_64-darwin"
-      } else {
-        assert(false, "Unknown host")
-      }
-
-      prefix = rebase_path("//buildtools/toolchain/clang+llvm-$host_suffix/bin",
+      prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
                            root_build_dir)
 
       cc = compiler_prefix + prefix + "/clang"
diff --git a/build/toolchain/linux/BUILD.gn b/build/toolchain/linux/BUILD.gn
index f92005dfe50..4925e15895c 100644
--- a/build/toolchain/linux/BUILD.gn
+++ b/build/toolchain/linux/BUILD.gn
@@ -60,7 +60,7 @@ gcc_toolchain("arm64") {
 }
 
 gcc_toolchain("clang_x86") {
-  prefix = rebase_path("//buildtools/toolchain/clang+llvm-x86_64-linux/bin",
+  prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
                        root_build_dir)
   cc = "${compiler_prefix}$prefix/clang"
   cxx = "${compiler_prefix}$prefix/clang++"
@@ -89,7 +89,7 @@ gcc_toolchain("x86") {
 }
 
 gcc_toolchain("clang_x64") {
-  prefix = rebase_path("//buildtools/toolchain/clang+llvm-x86_64-linux/bin",
+  prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
                        root_build_dir)
   cc = "${compiler_prefix}$prefix/clang"
   cxx = "${compiler_prefix}$prefix/clang++"
diff --git a/build/toolchain/mac/BUILD.gn b/build/toolchain/mac/BUILD.gn
index 15b802f6326..b291f0050b6 100644
--- a/build/toolchain/mac/BUILD.gn
+++ b/build/toolchain/mac/BUILD.gn
@@ -211,7 +211,7 @@ template("mac_toolchain") {
 mac_toolchain("clang_x64") {
   toolchain_cpu = "x64"
   toolchain_os = "mac"
-  prefix = rebase_path("//buildtools/toolchain/clang+llvm-x86_64-darwin/bin",
+  prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
                        root_build_dir)
   cc = "${goma_prefix}$prefix/clang"
   cxx = "${goma_prefix}$prefix/clang++"
@@ -224,7 +224,7 @@ mac_toolchain("clang_x64") {
 mac_toolchain("clang_i386") {
   toolchain_cpu = "i386"
   toolchain_os = "mac"
-  prefix = rebase_path("//buildtools/toolchain/clang+llvm-x86_64-darwin/bin",
+  prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
                        root_build_dir)
   cc = "${goma_prefix}$prefix/clang"
   cxx = "${goma_prefix}$prefix/clang++"
diff --git a/tools/android/VERSION_LINUX_NDK b/tools/android/VERSION_LINUX_NDK
deleted file mode 100644
index 9fff8ff1660..00000000000
--- a/tools/android/VERSION_LINUX_NDK
+++ /dev/null
@@ -1 +0,0 @@
-50bb526ee77fee88b9382d2bf48e7399751b98ae
diff --git a/tools/android/VERSION_LINUX_SDK b/tools/android/VERSION_LINUX_SDK
deleted file mode 100644
index d24f5c1f6ea..00000000000
--- a/tools/android/VERSION_LINUX_SDK
+++ /dev/null
@@ -1 +0,0 @@
-0d320c50b0ed188c7e1182388e2beb623a1d307d
diff --git a/tools/android/VERSION_MACOSX_NDK b/tools/android/VERSION_MACOSX_NDK
deleted file mode 100644
index aac8005d75f..00000000000
--- a/tools/android/VERSION_MACOSX_NDK
+++ /dev/null
@@ -1 +0,0 @@
-ed883dfaad6f27350eb3de426ccbf9abdc2943e8
diff --git a/tools/android/VERSION_MACOSX_SDK b/tools/android/VERSION_MACOSX_SDK
deleted file mode 100644
index 2441d725226..00000000000
--- a/tools/android/VERSION_MACOSX_SDK
+++ /dev/null
@@ -1 +0,0 @@
-fa5ea0ca1e0c7c2e40914f3202c7545de4dbca9c
diff --git a/tools/android/download_android_tools.py b/tools/android/download_android_tools.py
deleted file mode 100644
index e16989f3146..00000000000
--- a/tools/android/download_android_tools.py
+++ /dev/null
@@ -1,104 +0,0 @@
-#!/usr/bin/env python
-# Copyright 2017 The Dart project authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-# Downloads trimmed-down Android Tools from Google Cloud Storage and extracts
-# them to INSTALL_DIR, updating INSTALL_DIR/VERSION_* stamp files with current
-# version. Does nothing if INSTALL_DIR/VERSION_* are already up to date.
-
-import os
-import shutil
-import subprocess
-import sys
-import tarfile
-
-# Path constants. (All of these should be absolute paths.)
-THIS_DIR = os.path.abspath(os.path.dirname(__file__))
-DART_ROOT = os.path.abspath(os.path.join(THIS_DIR, '..', '..'))
-# Should be the same as in upload.py.
-INSTALL_DIR = os.path.join(DART_ROOT, 'third_party', 'android_tools')
-
-sys.path.insert(0, os.path.join(DART_ROOT, 'tools'))
-import find_depot_tools
-
-DEPOT_PATH = find_depot_tools.add_depot_tools_to_path()
-GSUTIL_PATH = os.path.join(DEPOT_PATH, 'gsutil.py')
-
-def RunCommand(command):
-  """Run command and return success (True) or failure."""
-
-  print 'Running %s' % (str(command))
-  if subprocess.call(command, shell=False) == 0:
-    return True
-  print 'Failed.'
-  return False
-
-
-def GetInstalledVersion(version_stamp):
-  version_file = os.path.join(INSTALL_DIR, version_stamp)
-  if not os.path.exists(version_file):
-    return None
-  with open(version_file) as f:
-    return f.read().strip()
-
-
-def VersionStampName(tools_name):
-  if sys.platform.startswith('linux'):
-    return 'VERSION_LINUX_' + tools_name.upper()
-  elif sys.platform == 'darwin':
-    return 'VERSION_MACOSX_' + tools_name.upper()
-  else:
-    print('NOTE: Will not download android tools. Unsupported platform: ' + sys.platform)
-    sys.exit(0)
-
-
-def UpdateTools(tools_name):
-  """Downloads zipped tools from Google Cloud Storage and extracts them,
-     stamping current version."""
-
-  # Read latest version.
-  version_stamp = VersionStampName(tools_name)
-  version = ''
-  with open(os.path.join(THIS_DIR, version_stamp)) as f:
-    version = f.read().strip()
-  # Return if installed binaries are up to date.
-  if version == GetInstalledVersion(version_stamp):
-    return
-
-  # Remove the old install directory checked out from git.
-  if os.path.exists(os.path.join(INSTALL_DIR, '.git')):
-    shutil.rmtree(INSTALL_DIR)
-  # Make sure that the install directory exists.
-  if not os.path.exists(INSTALL_DIR):
-    os.mkdir(INSTALL_DIR)
-  # Remove current installation.
-  tools_root = os.path.join(INSTALL_DIR, tools_name)
-  if os.path.exists(tools_root):
-    shutil.rmtree(tools_root)
-
-  # Download tools from GCS.
-  archive_path = os.path.join(INSTALL_DIR, tools_name + '.tar.gz')
-  download_cmd = ['python', GSUTIL_PATH, 'cp',
-                  'gs://mojo/android/tool/%s.tar.gz' % version,
-                  archive_path]
-  if not RunCommand(download_cmd):
-    print ('WARNING: Failed to download Android tools.')
-    return
-
-  print "Extracting Android tools (" + tools_name + ")"
-  with tarfile.open(archive_path) as arch:
-    arch.extractall(INSTALL_DIR)
-  os.remove(archive_path)
-  # Write version as the last step.
-  with open(os.path.join(INSTALL_DIR, version_stamp), 'w+') as f:
-    f.write('%s\n' % version)
-
-
-def main():
-  UpdateTools('sdk')
-  UpdateTools('ndk')
-
-
-if __name__ == '__main__':
-  sys.exit(main())
\ No newline at end of file
diff --git a/tools/build.py b/tools/build.py
index 29c081f3899..90dfcd7e9f2 100755
--- a/tools/build.py
+++ b/tools/build.py
@@ -131,7 +131,7 @@ def ProcessOptions(options, args):
       if os_name != 'android':
         print "Unsupported target os %s" % os_name
         return False
-      if not HOST_OS in ['linux', 'macos']:
+      if not HOST_OS in ['linux']:
         print ("Cross-compilation to %s is not supported on host os %s."
                % (os_name, HOST_OS))
         return False
diff --git a/tools/buildtools/linux64/clang-format b/tools/buildtools/linux64/clang-format
deleted file mode 100755
index 715ff745bb6..00000000000
--- a/tools/buildtools/linux64/clang-format
+++ /dev/null
@@ -1,20 +0,0 @@
-#!/usr/bin/env python
-# Copyright 2017 The Dart project authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-"""Forwards to the clang-format for the Linux toolchain."""
-
-import os
-import subprocess
-import sys
-
-DART_ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
-TOOLCHAIN = os.path.join(DART_ROOT, 'buildtools', 'toolchain')
-CLANG_FORMAT = os.path.join(TOOLCHAIN, 'clang+llvm-x86_64-linux', 'bin', 'clang-format')
-
-def main(argv):
-  return subprocess.call([CLANG_FORMAT] + argv[1:])
-
-if __name__ == '__main__':
-  sys.exit(main(sys.argv))
diff --git a/tools/buildtools/mac/clang-format b/tools/buildtools/mac/clang-format
deleted file mode 100755
index 39549a91daa..00000000000
--- a/tools/buildtools/mac/clang-format
+++ /dev/null
@@ -1,20 +0,0 @@
-#!/usr/bin/env python
-# Copyright 2017 The Dart project authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-"""Forwards to the clang-format for the MacOS toolchain."""
-
-import os
-import subprocess
-import sys
-
-DART_ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
-TOOLCHAIN = os.path.join(DART_ROOT, 'buildtools', 'toolchain')
-CLANG_FORMAT = os.path.join(TOOLCHAIN, 'clang+llvm-x86_64-darwin', 'bin', 'clang-format')
-
-def main(argv):
-  return subprocess.call([CLANG_FORMAT] + argv[1:])
-
-if __name__ == '__main__':
-  sys.exit(main(sys.argv))
diff --git a/tools/buildtools/update.py b/tools/buildtools/update.py
deleted file mode 100755
index 6d676293aa4..00000000000
--- a/tools/buildtools/update.py
+++ /dev/null
@@ -1,88 +0,0 @@
-#!/usr/bin/env python
-# Copyright 2017 The Dart project authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-"""Pulls down tools required to build Dart."""
-
-import os
-import subprocess
-import shutil
-import sys
-
-THIS_DIR = os.path.abspath(os.path.dirname(__file__))
-DART_ROOT = os.path.abspath(os.path.join(THIS_DIR, '..', '..'))
-BUILDTOOLS = os.path.join(DART_ROOT, 'buildtools')
-TOOLS_BUILDTOOLS = os.path.join(DART_ROOT, 'tools', 'buildtools')
-
-sys.path.insert(0, os.path.join(DART_ROOT, 'tools'))
-import find_depot_tools
-
-DEPOT_PATH = find_depot_tools.add_depot_tools_to_path()
-
-
-def Update():
-  path = os.path.join(BUILDTOOLS, 'update.sh')
-  return subprocess.call(['/bin/bash', path, '--toolchain', '--gn'], cwd=DART_ROOT)
-
-
-def UpdateGNOnWindows():
-  sha1_file = os.path.join(BUILDTOOLS, 'win', 'gn.exe.sha1')
-  downloader_script = os.path.join(DEPOT_PATH, 'download_from_google_storage.py')
-  download_cmd = [
-    'python',
-    downloader_script,
-    '--no_auth',
-    '--no_resume',
-    '--quiet',
-    '--platform=win*',
-    '--bucket',
-    'chromium-gn',
-    '-s',
-    sha1_file
-  ]
-  return subprocess.call(download_cmd)
-
-
-def UpdateClangFormatOnWindows():
-  sha1_file = os.path.join(TOOLS_BUILDTOOLS, 'win', 'clang-format.exe.sha1')
-  output_dir = os.path.join(BUILDTOOLS, 'win', 'clang-format.exe')
-  downloader_script = os.path.join(DEPOT_PATH, 'download_from_google_storage.py')
-  download_cmd = [
-    'python',
-    downloader_script,
-    '--no_auth',
-    '--no_resume',
-    '--quiet',
-    '--platform=win',
-    '--bucket',
-    'chromium-clang-format',
-    '-s',
-    sha1_file,
-    '-o',
-    output_dir
-  ]
-  return subprocess.call(download_cmd)
-
-
-def CopyClangFormatScripts():
-  linux_script = os.path.join(TOOLS_BUILDTOOLS, 'linux64', 'clang-format')
-  mac_script = os.path.join(TOOLS_BUILDTOOLS, 'mac', 'clang-format')
-  linux_dest = os.path.join(BUILDTOOLS, 'linux64', 'clang-format')
-  mac_dest = os.path.join(BUILDTOOLS, 'mac', 'clang-format')
-  shutil.copy2(linux_script, linux_dest)
-  shutil.copy2(mac_script, mac_dest)
-
-
-def main(argv):
-  if sys.platform.startswith('win'):
-    result = UpdateGNOnWindows()
-    if result != 0:
-      return result
-    return UpdateClangFormatOnWindows()
-  CopyClangFormatScripts()
-  return Update()
-
-
-if __name__ == '__main__':
-  sys.exit(main(sys.argv))
diff --git a/tools/buildtools/win/clang-format.exe.sha1 b/tools/buildtools/win/clang-format.exe.sha1
deleted file mode 100644
index a78543133b6..00000000000
--- a/tools/buildtools/win/clang-format.exe.sha1
+++ /dev/null
@@ -1,2 +0,0 @@
-6ddedd571c56b8c184f30a3c1fc36984e8c10ccd
-
diff --git a/tools/clang/scripts/update.py b/tools/clang/scripts/update.py
new file mode 100755
index 00000000000..100bdec5cc8
--- /dev/null
+++ b/tools/clang/scripts/update.py
@@ -0,0 +1,909 @@
+#!/usr/bin/env python
+# Copyright (c) 2012 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""This script is used to download prebuilt clang binaries.
+
+It is also used by package.py to build the prebuilt clang binaries."""
+
+import argparse
+import distutils.spawn
+import glob
+import os
+import pipes
+import re
+import shutil
+import subprocess
+import stat
+import sys
+import tarfile
+import tempfile
+import time
+import urllib2
+import zipfile
+
+
+# Do NOT CHANGE this if you don't know what you're doing -- see
+# https://chromium.googlesource.com/chromium/src/+/master/docs/updating_clang.md
+# Reverting problematic clang rolls is safe, though.
+CLANG_REVISION = '282487'
+
+use_head_revision = 'LLVM_FORCE_HEAD_REVISION' in os.environ
+if use_head_revision:
+  CLANG_REVISION = 'HEAD'
+
+# This is incremented when pushing a new build of Clang at the same revision.
+CLANG_SUB_REVISION=1
+
+PACKAGE_VERSION = "%s-%s" % (CLANG_REVISION, CLANG_SUB_REVISION)
+
+# Path constants. (All of these should be absolute paths.)
+THIS_DIR = os.path.abspath(os.path.dirname(__file__))
+CHROMIUM_DIR = os.path.abspath(os.path.join(THIS_DIR, '..', '..', '..'))
+THIRD_PARTY_DIR = os.path.join(CHROMIUM_DIR, 'third_party')
+LLVM_DIR = os.path.join(THIRD_PARTY_DIR, 'llvm')
+LLVM_BOOTSTRAP_DIR = os.path.join(THIRD_PARTY_DIR, 'llvm-bootstrap')
+LLVM_BOOTSTRAP_INSTALL_DIR = os.path.join(THIRD_PARTY_DIR,
+                                          'llvm-bootstrap-install')
+LLVM_LTO_GOLD_PLUGIN_DIR = os.path.join(THIRD_PARTY_DIR, 'llvm-lto-gold-plugin')
+CHROME_TOOLS_SHIM_DIR = os.path.join(LLVM_DIR, 'tools', 'chrometools')
+LLVM_BUILD_DIR = os.path.join(CHROMIUM_DIR, 'third_party', 'llvm-build',
+                              'Release+Asserts')
+COMPILER_RT_BUILD_DIR = os.path.join(LLVM_BUILD_DIR, 'compiler-rt')
+CLANG_DIR = os.path.join(LLVM_DIR, 'tools', 'clang')
+LLD_DIR = os.path.join(LLVM_DIR, 'tools', 'lld')
+# compiler-rt is built as part of the regular LLVM build on Windows to get
+# the 64-bit runtime, and out-of-tree elsewhere.
+# TODO(thakis): Try to unify this.
+if sys.platform == 'win32':
+  COMPILER_RT_DIR = os.path.join(LLVM_DIR, 'projects', 'compiler-rt')
+else:
+  COMPILER_RT_DIR = os.path.join(LLVM_DIR, 'compiler-rt')
+LIBCXX_DIR = os.path.join(LLVM_DIR, 'projects', 'libcxx')
+LIBCXXABI_DIR = os.path.join(LLVM_DIR, 'projects', 'libcxxabi')
+LLVM_BUILD_TOOLS_DIR = os.path.abspath(
+    os.path.join(LLVM_DIR, '..', 'llvm-build-tools'))
+STAMP_FILE = os.path.normpath(
+    os.path.join(LLVM_DIR, '..', 'llvm-build', 'cr_build_revision'))
+BINUTILS_DIR = os.path.join(THIRD_PARTY_DIR, 'binutils')
+BINUTILS_BIN_DIR = os.path.join(BINUTILS_DIR, BINUTILS_DIR,
+                                'Linux_x64', 'Release', 'bin')
+BFD_PLUGINS_DIR = os.path.join(BINUTILS_DIR, 'Linux_x64', 'Release',
+                               'lib', 'bfd-plugins')
+VERSION = '4.0.0'
+ANDROID_NDK_DIR = os.path.join(
+    CHROMIUM_DIR, 'third_party', 'android_tools', 'ndk')
+
+# URL for pre-built binaries.
+CDS_URL = os.environ.get('CDS_CLANG_BUCKET_OVERRIDE',
+    'https://commondatastorage.googleapis.com/chromium-browser-clang')
+
+LLVM_REPO_URL='https://llvm.org/svn/llvm-project'
+if 'LLVM_REPO_URL' in os.environ:
+  LLVM_REPO_URL = os.environ['LLVM_REPO_URL']
+
+# Bump after VC updates.
+DIA_DLL = {
+  '2013': 'msdia120.dll',
+  '2015': 'msdia140.dll',
+}
+
+
+def DownloadUrl(url, output_file):
+  """Download url into output_file."""
+  CHUNK_SIZE = 4096
+  TOTAL_DOTS = 10
+  num_retries = 3
+  retry_wait_s = 5  # Doubled at each retry.
+
+  while True:
+    try:
+      sys.stdout.write('Downloading %s ' % url)
+      sys.stdout.flush()
+      response = urllib2.urlopen(url)
+      total_size = int(response.info().getheader('Content-Length').strip())
+      bytes_done = 0
+      dots_printed = 0
+      while True:
+        chunk = response.read(CHUNK_SIZE)
+        if not chunk:
+          break
+        output_file.write(chunk)
+        bytes_done += len(chunk)
+        num_dots = TOTAL_DOTS * bytes_done / total_size
+        sys.stdout.write('.' * (num_dots - dots_printed))
+        sys.stdout.flush()
+        dots_printed = num_dots
+      if bytes_done != total_size:
+        raise urllib2.URLError("only got %d of %d bytes" %
+                               (bytes_done, total_size))
+      print ' Done.'
+      return
+    except urllib2.URLError as e:
+      sys.stdout.write('\n')
+      print e
+      if num_retries == 0 or isinstance(e, urllib2.HTTPError) and e.code == 404:
+        raise e
+      num_retries -= 1
+      print 'Retrying in %d s ...' % retry_wait_s
+      time.sleep(retry_wait_s)
+      retry_wait_s *= 2
+
+
+def EnsureDirExists(path):
+  if not os.path.exists(path):
+    print "Creating directory %s" % path
+    os.makedirs(path)
+
+
+def DownloadAndUnpack(url, output_dir):
+  with tempfile.TemporaryFile() as f:
+    DownloadUrl(url, f)
+    f.seek(0)
+    EnsureDirExists(output_dir)
+    if url.endswith('.zip'):
+      zipfile.ZipFile(f).extractall(path=output_dir)
+    else:
+      tarfile.open(mode='r:gz', fileobj=f).extractall(path=output_dir)
+
+
+def ReadStampFile(path=STAMP_FILE):
+  """Return the contents of the stamp file, or '' if it doesn't exist."""
+  try:
+    with open(path, 'r') as f:
+      return f.read().rstrip()
+  except IOError:
+    return ''
+
+
+def WriteStampFile(s, path=STAMP_FILE):
+  """Write s to the stamp file."""
+  EnsureDirExists(os.path.dirname(path))
+  with open(path, 'w') as f:
+    f.write(s)
+    f.write('\n')
+
+
+def GetSvnRevision(svn_repo):
+  """Returns current revision of the svn repo at svn_repo."""
+  if sys.platform == 'darwin':
+    # mac_files toolchain must be set for hermetic builds.
+    root = os.path.dirname(os.path.dirname(os.path.dirname(
+        os.path.dirname(__file__))))
+    sys.path.append(os.path.join(root, 'build'))
+    import mac_toolchain
+
+    mac_toolchain.SetToolchainEnvironment()
+  svn_info = subprocess.check_output('svn info ' + svn_repo, shell=True)
+  m = re.search(r'Revision: (\d+)', svn_info)
+  return m.group(1)
+
+
+def RmTree(dir):
+  """Delete dir."""
+  def ChmodAndRetry(func, path, _):
+    # Subversion can leave read-only files around.
+    if not os.access(path, os.W_OK):
+      os.chmod(path, stat.S_IWUSR)
+      return func(path)
+    raise
+
+  shutil.rmtree(dir, onerror=ChmodAndRetry)
+
+
+def RmCmakeCache(dir):
+  """Delete CMake cache related files from dir."""
+  for dirpath, dirs, files in os.walk(dir):
+    if 'CMakeCache.txt' in files:
+      os.remove(os.path.join(dirpath, 'CMakeCache.txt'))
+    if 'CMakeFiles' in dirs:
+      RmTree(os.path.join(dirpath, 'CMakeFiles'))
+
+
+def RunCommand(command, msvc_arch=None, env=None, fail_hard=True):
+  """Run command and return success (True) or failure; or if fail_hard is
+     True, exit on failure.  If msvc_arch is set, runs the command in a
+     shell with the msvc tools for that architecture."""
+
+  if msvc_arch and sys.platform == 'win32':
+    command = GetVSVersion().SetupScript(msvc_arch) + ['&&'] + command
+
+  # https://docs.python.org/2/library/subprocess.html:
+  # "On Unix with shell=True [...] if args is a sequence, the first item
+  # specifies the command string, and any additional items will be treated as
+  # additional arguments to the shell itself.  That is to say, Popen does the
+  # equivalent of:
+  #   Popen(['/bin/sh', '-c', args[0], args[1], ...])"
+  #
+  # We want to pass additional arguments to command[0], not to the shell,
+  # so manually join everything into a single string.
+  # Annoyingly, for "svn co url c:\path", pipes.quote() thinks that it should
+  # quote c:\path but svn can't handle quoted paths on Windows.  Since on
+  # Windows follow-on args are passed to args[0] instead of the shell, don't
+  # do the single-string transformation there.
+  if sys.platform != 'win32':
+    command = ' '.join([pipes.quote(c) for c in command])
+  print 'Running', command
+  if subprocess.call(command, env=env, shell=True) == 0:
+    return True
+  print 'Failed.'
+  if fail_hard:
+    sys.exit(1)
+  return False
+
+
+def CopyFile(src, dst):
+  """Copy a file from src to dst."""
+  print "Copying %s to %s" % (src, dst)
+  shutil.copy(src, dst)
+
+
+def CopyDirectoryContents(src, dst, filename_filter=None):
+  """Copy the files from directory src to dst
+  with an optional filename filter."""
+  dst = os.path.realpath(dst)  # realpath() in case dst ends in /..
+  EnsureDirExists(dst)
+  for root, _, files in os.walk(src):
+    for f in files:
+      if filename_filter and not re.match(filename_filter, f):
+        continue
+      CopyFile(os.path.join(root, f), dst)
+
+
+def Checkout(name, url, dir):
+  """Checkout the SVN module at url into dir. Use name for the log message."""
+  print "Checking out %s r%s into '%s'" % (name, CLANG_REVISION, dir)
+
+  command = ['svn', 'checkout', '--force', url + '@' + CLANG_REVISION, dir]
+  if RunCommand(command, fail_hard=False):
+    return
+
+  if os.path.isdir(dir):
+    print "Removing %s." % (dir)
+    RmTree(dir)
+
+  print "Retrying."
+  RunCommand(command)
+
+
+def DeleteChromeToolsShim():
+  OLD_SHIM_DIR = os.path.join(LLVM_DIR, 'tools', 'zzz-chrometools')
+  shutil.rmtree(OLD_SHIM_DIR, ignore_errors=True)
+  shutil.rmtree(CHROME_TOOLS_SHIM_DIR, ignore_errors=True)
+
+
+def CreateChromeToolsShim():
+  """Hooks the Chrome tools into the LLVM build.
+
+  Several Chrome tools have dependencies on LLVM/Clang libraries. The LLVM build
+  detects implicit tools in the tools subdirectory, so this helper install a
+  shim CMakeLists.txt that forwards to the real directory for the Chrome tools.
+
+  Note that the shim directory name intentionally has no - or _. The implicit
+  tool detection logic munges them in a weird way."""
+  assert not any(i in os.path.basename(CHROME_TOOLS_SHIM_DIR) for i in '-_')
+  os.mkdir(CHROME_TOOLS_SHIM_DIR)
+  with file(os.path.join(CHROME_TOOLS_SHIM_DIR, 'CMakeLists.txt'), 'w') as f:
+    f.write('# Automatically generated by tools/clang/scripts/update.py. ' +
+            'Do not edit.\n')
+    f.write('# Since tools/clang is located in another directory, use the \n')
+    f.write('# two arg version to specify where build artifacts go. CMake\n')
+    f.write('# disallows reuse of the same binary dir for multiple source\n')
+    f.write('# dirs, so the build artifacts need to go into a subdirectory.\n')
+    f.write('# dirs, so the build artifacts need to go into a subdirectory.\n')
+    f.write('if (CHROMIUM_TOOLS_SRC)\n')
+    f.write('  add_subdirectory(${CHROMIUM_TOOLS_SRC} ' +
+              '${CMAKE_CURRENT_BINARY_DIR}/a)\n')
+    f.write('endif (CHROMIUM_TOOLS_SRC)\n')
+
+
+def DownloadHostGcc(args):
+  """Downloads gcc 4.8.5 and makes sure args.gcc_toolchain is set."""
+  if not sys.platform.startswith('linux') or args.gcc_toolchain:
+    return
+  # Unconditionally download a prebuilt gcc to guarantee the included libstdc++
+  # works on Ubuntu Precise.
+  gcc_dir = os.path.join(LLVM_BUILD_TOOLS_DIR, 'gcc485precise')
+  if not os.path.exists(gcc_dir):
+    print 'Downloading pre-built GCC 4.8.5...'
+    DownloadAndUnpack(
+        CDS_URL + '/tools/gcc485precise.tgz', LLVM_BUILD_TOOLS_DIR)
+  args.gcc_toolchain = gcc_dir
+
+
+def AddCMakeToPath():
+  """Download CMake and add it to PATH."""
+  if sys.platform == 'win32':
+    zip_name = 'cmake-3.4.3-win32-x86.zip'
+    cmake_dir = os.path.join(LLVM_BUILD_TOOLS_DIR,
+                             'cmake-3.4.3-win32-x86', 'bin')
+  else:
+    suffix = 'Darwin' if sys.platform == 'darwin' else 'Linux'
+    zip_name = 'cmake343_%s.tgz' % suffix
+    cmake_dir = os.path.join(LLVM_BUILD_TOOLS_DIR, 'cmake343', 'bin')
+  if not os.path.exists(cmake_dir):
+    DownloadAndUnpack(CDS_URL + '/tools/' + zip_name, LLVM_BUILD_TOOLS_DIR)
+  os.environ['PATH'] = cmake_dir + os.pathsep + os.environ.get('PATH', '')
+
+
+def AddGnuWinToPath():
+  """Download some GNU win tools and add them to PATH."""
+  if sys.platform != 'win32':
+    return
+
+  gnuwin_dir = os.path.join(LLVM_BUILD_TOOLS_DIR, 'gnuwin')
+  GNUWIN_VERSION = '5'
+  GNUWIN_STAMP = os.path.join(gnuwin_dir, 'stamp')
+  if ReadStampFile(GNUWIN_STAMP) == GNUWIN_VERSION:
+    print 'GNU Win tools already up to date.'
+  else:
+    zip_name = 'gnuwin-%s.zip' % GNUWIN_VERSION
+    DownloadAndUnpack(CDS_URL + '/tools/' + zip_name, LLVM_BUILD_TOOLS_DIR)
+    WriteStampFile(GNUWIN_VERSION, GNUWIN_STAMP)
+
+  os.environ['PATH'] = gnuwin_dir + os.pathsep + os.environ.get('PATH', '')
+
+
+vs_version = None
+def GetVSVersion():
+  global vs_version
+  if vs_version:
+    return vs_version
+
+  # Try using the toolchain in depot_tools.
+  # This sets environment variables used by SelectVisualStudioVersion below.
+  sys.path.append(os.path.join(CHROMIUM_DIR, 'build'))
+  import vs_toolchain
+  vs_toolchain.SetEnvironmentAndGetRuntimeDllDirs()
+
+  # Use gyp to find the MSVS installation, either in depot_tools as per above,
+  # or a system-wide installation otherwise.
+  sys.path.append(os.path.join(CHROMIUM_DIR, 'tools', 'gyp', 'pylib'))
+  import gyp.MSVSVersion
+  vs_version = gyp.MSVSVersion.SelectVisualStudioVersion(
+      vs_toolchain.GetVisualStudioVersion())
+  return vs_version
+
+
+def CopyDiaDllTo(target_dir):
+  # This script always wants to use the 64-bit msdia*.dll.
+  dia_path = os.path.join(GetVSVersion().Path(), 'DIA SDK', 'bin', 'amd64')
+  dia_dll = os.path.join(dia_path, DIA_DLL[GetVSVersion().ShortName()])
+  CopyFile(dia_dll, target_dir)
+
+
+def VeryifyVersionOfBuiltClangMatchesVERSION():
+  """Checks that `clang --version` outputs VERSION.  If this fails, VERSION
+  in this file is out-of-date and needs to be updated (possibly in an
+  `if use_head_revision:` block in main() first)."""
+  clang = os.path.join(LLVM_BUILD_DIR, 'bin', 'clang')
+  if sys.platform == 'win32':
+    # TODO: Parse `clang-cl /?` output for built clang's version and check that
+    # to check the binary we're actually shipping? But clang-cl.exe is just
+    # a copy of clang.exe, so this does check the same thing.
+    clang += '.exe'
+  version_out = subprocess.check_output([clang, '--version'])
+  version_out = re.match(r'clang version ([0-9.]+)', version_out).group(1)
+  if version_out != VERSION:
+    print ('unexpected clang version %s (not %s), update VERSION in update.py'
+           % (version_out, VERSION))
+    sys.exit(1)
+
+
+def UpdateClang(args):
+  print 'Updating Clang to %s...' % PACKAGE_VERSION
+
+  need_gold_plugin = 'LLVM_DOWNLOAD_GOLD_PLUGIN' in os.environ or (
+      sys.platform.startswith('linux') and
+      'buildtype=Official' in os.environ.get('GYP_DEFINES', '') and
+      'branding=Chrome' in os.environ.get('GYP_DEFINES', ''))
+
+  if ReadStampFile() == PACKAGE_VERSION and not args.force_local_build:
+    print 'Clang is already up to date.'
+    if not need_gold_plugin or os.path.exists(
+        os.path.join(LLVM_BUILD_DIR, "lib/LLVMgold.so")):
+      return 0
+
+  # Reset the stamp file in case the build is unsuccessful.
+  WriteStampFile('')
+
+  if not args.force_local_build:
+    cds_file = "clang-%s.tgz" %  PACKAGE_VERSION
+    if sys.platform == 'win32' or sys.platform == 'cygwin':
+      cds_full_url = CDS_URL + '/Win/' + cds_file
+    elif sys.platform == 'darwin':
+      cds_full_url = CDS_URL + '/Mac/' + cds_file
+    else:
+      assert sys.platform.startswith('linux')
+      cds_full_url = CDS_URL + '/Linux_x64/' + cds_file
+
+    print 'Downloading prebuilt clang'
+    if os.path.exists(LLVM_BUILD_DIR):
+      RmTree(LLVM_BUILD_DIR)
+    try:
+      DownloadAndUnpack(cds_full_url, LLVM_BUILD_DIR)
+      print 'clang %s unpacked' % PACKAGE_VERSION
+      if sys.platform == 'win32':
+        CopyDiaDllTo(os.path.join(LLVM_BUILD_DIR, 'bin'))
+      # Download the gold plugin if requested to by an environment variable.
+      # This is used by the CFI ClusterFuzz bot, and it's required for official
+      # builds on linux.
+      if need_gold_plugin:
+        RunCommand(['python', CHROMIUM_DIR+'/build/download_gold_plugin.py'])
+      WriteStampFile(PACKAGE_VERSION)
+      return 0
+    except urllib2.URLError:
+      print 'Failed to download prebuilt clang %s' % cds_file
+      print 'Use --force-local-build if you want to build locally.'
+      print 'Exiting.'
+      return 1
+
+  if args.with_android and not os.path.exists(ANDROID_NDK_DIR):
+    print 'Android NDK not found at ' + ANDROID_NDK_DIR
+    print 'The Android NDK is needed to build a Clang whose -fsanitize=address'
+    print 'works on Android. See '
+    print 'https://www.chromium.org/developers/how-tos/android-build-instructions'
+    print 'for how to install the NDK, or pass --without-android.'
+    return 1
+
+  DownloadHostGcc(args)
+  AddCMakeToPath()
+  AddGnuWinToPath()
+
+  DeleteChromeToolsShim()
+
+  Checkout('LLVM', LLVM_REPO_URL + '/llvm/trunk', LLVM_DIR)
+  Checkout('Clang', LLVM_REPO_URL + '/cfe/trunk', CLANG_DIR)
+  if sys.platform == 'win32' or use_head_revision:
+    Checkout('LLD', LLVM_REPO_URL + '/lld/trunk', LLD_DIR)
+  Checkout('compiler-rt', LLVM_REPO_URL + '/compiler-rt/trunk', COMPILER_RT_DIR)
+  if sys.platform == 'darwin':
+    # clang needs a libc++ checkout, else -stdlib=libc++ won't find includes
+    # (i.e. this is needed for bootstrap builds).
+    Checkout('libcxx', LLVM_REPO_URL + '/libcxx/trunk', LIBCXX_DIR)
+    # We used to check out libcxxabi on OS X; we no longer need that.
+    if os.path.exists(LIBCXXABI_DIR):
+      RmTree(LIBCXXABI_DIR)
+
+  cc, cxx = None, None
+  libstdcpp = None
+  if args.gcc_toolchain:  # This option is only used on Linux.
+    # Use the specified gcc installation for building.
+    cc = os.path.join(args.gcc_toolchain, 'bin', 'gcc')
+    cxx = os.path.join(args.gcc_toolchain, 'bin', 'g++')
+
+    if not os.access(cc, os.X_OK):
+      print 'Invalid --gcc-toolchain: "%s"' % args.gcc_toolchain
+      print '"%s" does not appear to be valid.' % cc
+      return 1
+
+    # Set LD_LIBRARY_PATH to make auxiliary targets (tablegen, bootstrap
+    # compiler, etc.) find the .so.
+    libstdcpp = subprocess.check_output(
+        [cxx, '-print-file-name=libstdc++.so.6']).rstrip()
+    os.environ['LD_LIBRARY_PATH'] = os.path.dirname(libstdcpp)
+
+  cflags = []
+  cxxflags = []
+  ldflags = []
+
+  base_cmake_args = ['-GNinja',
+                     '-DCMAKE_BUILD_TYPE=Release',
+                     '-DLLVM_ENABLE_ASSERTIONS=ON',
+                     '-DLLVM_ENABLE_THREADS=OFF',
+                     '-DLLVM_ENABLE_TIMESTAMPS=OFF',
+                     # Statically link MSVCRT to avoid DLL dependencies.
+                     '-DLLVM_USE_CRT_RELEASE=MT',
+                     ]
+
+  binutils_incdir = ''
+  if sys.platform.startswith('linux'):
+    binutils_incdir = os.path.join(BINUTILS_DIR, 'Linux_x64/Release/include')
+
+  if args.bootstrap:
+    print 'Building bootstrap compiler'
+    EnsureDirExists(LLVM_BOOTSTRAP_DIR)
+    os.chdir(LLVM_BOOTSTRAP_DIR)
+    bootstrap_args = base_cmake_args + [
+        '-DLLVM_BINUTILS_INCDIR=' + binutils_incdir,
+        '-DLLVM_TARGETS_TO_BUILD=host',
+        '-DCMAKE_INSTALL_PREFIX=' + LLVM_BOOTSTRAP_INSTALL_DIR,
+        '-DCMAKE_C_FLAGS=' + ' '.join(cflags),
+        '-DCMAKE_CXX_FLAGS=' + ' '.join(cxxflags),
+        ]
+    if cc is not None:  bootstrap_args.append('-DCMAKE_C_COMPILER=' + cc)
+    if cxx is not None: bootstrap_args.append('-DCMAKE_CXX_COMPILER=' + cxx)
+    RmCmakeCache('.')
+    RunCommand(['cmake'] + bootstrap_args + [LLVM_DIR], msvc_arch='x64')
+    RunCommand(['ninja'], msvc_arch='x64')
+    if args.run_tests:
+      if sys.platform == 'win32':
+        CopyDiaDllTo(os.path.join(LLVM_BOOTSTRAP_DIR, 'bin'))
+      RunCommand(['ninja', 'check-all'], msvc_arch='x64')
+    RunCommand(['ninja', 'install'], msvc_arch='x64')
+    if args.gcc_toolchain:
+      # Copy that gcc's stdlibc++.so.6 to the build dir, so the bootstrap
+      # compiler can start.
+      CopyFile(libstdcpp, os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'lib'))
+
+    if sys.platform == 'win32':
+      cc = os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'bin', 'clang-cl.exe')
+      cxx = os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'bin', 'clang-cl.exe')
+      # CMake has a hard time with backslashes in compiler paths:
+      # https://stackoverflow.com/questions/13050827
+      cc = cc.replace('\\', '/')
+      cxx = cxx.replace('\\', '/')
+    else:
+      cc = os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'bin', 'clang')
+      cxx = os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'bin', 'clang++')
+
+    if args.gcc_toolchain:
+      # Tell the bootstrap compiler to use a specific gcc prefix to search
+      # for standard library headers and shared object files.
+      cflags = ['--gcc-toolchain=' + args.gcc_toolchain]
+      cxxflags = ['--gcc-toolchain=' + args.gcc_toolchain]
+    print 'Building final compiler'
+
+  # Build LLVM gold plugin with LTO. That speeds up the linker by ~10%.
+  # We only use LTO for Linux now.
+  if args.bootstrap and args.lto_gold_plugin:
+    print 'Building LTO LLVM Gold plugin'
+    if os.path.exists(LLVM_LTO_GOLD_PLUGIN_DIR):
+      RmTree(LLVM_LTO_GOLD_PLUGIN_DIR)
+    EnsureDirExists(LLVM_LTO_GOLD_PLUGIN_DIR)
+    os.chdir(LLVM_LTO_GOLD_PLUGIN_DIR)
+
+    # Create a symlink to LLVMgold.so build in the previous step so that ar
+    # and ranlib could find it while linking LLVMgold.so with LTO.
+    EnsureDirExists(BFD_PLUGINS_DIR)
+    RunCommand(['ln', '-sf',
+                os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'lib', 'LLVMgold.so'),
+                os.path.join(BFD_PLUGINS_DIR, 'LLVMgold.so')])
+
+    lto_cflags = ['-flto']
+    lto_ldflags = ['-fuse-ld=gold']
+    if args.gcc_toolchain:
+      # Tell the bootstrap compiler to use a specific gcc prefix to search
+      # for standard library headers and shared object files.
+      lto_cflags += ['--gcc-toolchain=' + args.gcc_toolchain]
+    lto_cmake_args = base_cmake_args + [
+        '-DLLVM_BINUTILS_INCDIR=' + binutils_incdir,
+        '-DCMAKE_C_COMPILER=' + cc,
+        '-DCMAKE_CXX_COMPILER=' + cxx,
+        '-DCMAKE_C_FLAGS=' + ' '.join(lto_cflags),
+        '-DCMAKE_CXX_FLAGS=' + ' '.join(lto_cflags),
+        '-DCMAKE_EXE_LINKER_FLAGS=' + ' '.join(lto_ldflags),
+        '-DCMAKE_SHARED_LINKER_FLAGS=' + ' '.join(lto_ldflags),
+        '-DCMAKE_MODULE_LINKER_FLAGS=' + ' '.join(lto_ldflags)]
+
+    # We need to use the proper binutils which support LLVM Gold plugin.
+    lto_env = os.environ.copy()
+    lto_env['PATH'] = BINUTILS_BIN_DIR + os.pathsep + lto_env.get('PATH', '')
+
+    RmCmakeCache('.')
+    RunCommand(['cmake'] + lto_cmake_args + [LLVM_DIR], env=lto_env)
+    RunCommand(['ninja', 'LLVMgold'], env=lto_env)
+
+
+  # LLVM uses C++11 starting in llvm 3.5. On Linux, this means libstdc++4.7+ is
+  # needed, on OS X it requires libc++. clang only automatically links to libc++
+  # when targeting OS X 10.9+, so add stdlib=libc++ explicitly so clang can run
+  # on OS X versions as old as 10.7.
+  deployment_target = ''
+
+  if sys.platform == 'darwin' and args.bootstrap:
+    # When building on 10.9, /usr/include usually doesn't exist, and while
+    # Xcode's clang automatically sets a sysroot, self-built clangs don't.
+    cflags = ['-isysroot', subprocess.check_output(
+        ['xcrun', '--show-sdk-path']).rstrip()]
+    cxxflags = ['-stdlib=libc++'] + cflags
+    ldflags += ['-stdlib=libc++']
+    deployment_target = '10.7'
+    # Running libc++ tests takes a long time. Since it was only needed for
+    # the install step above, don't build it as part of the main build.
+    # This makes running package.py over 10% faster (30 min instead of 34 min)
+    RmTree(LIBCXX_DIR)
+
+  # Build clang.
+
+  # If building at head, define a macro that plugins can use for #ifdefing
+  # out code that builds at head, but not at CLANG_REVISION or vice versa.
+  if use_head_revision:
+    cflags += ['-DLLVM_FORCE_HEAD_REVISION']
+    cxxflags += ['-DLLVM_FORCE_HEAD_REVISION']
+
+  CreateChromeToolsShim()
+
+  deployment_env = None
+  if deployment_target:
+    deployment_env = os.environ.copy()
+    deployment_env['MACOSX_DEPLOYMENT_TARGET'] = deployment_target
+
+  cmake_args = []
+  # TODO(thakis): Unconditionally append this to base_cmake_args instead once
+  # compiler-rt can build with clang-cl on Windows (http://llvm.org/PR23698)
+  cc_args = base_cmake_args if sys.platform != 'win32' else cmake_args
+  if cc is not None:  cc_args.append('-DCMAKE_C_COMPILER=' + cc)
+  if cxx is not None: cc_args.append('-DCMAKE_CXX_COMPILER=' + cxx)
+  cmake_args += base_cmake_args + [
+      '-DLLVM_BINUTILS_INCDIR=' + binutils_incdir,
+      '-DCMAKE_C_FLAGS=' + ' '.join(cflags),
+      '-DCMAKE_CXX_FLAGS=' + ' '.join(cxxflags),
+      '-DCMAKE_EXE_LINKER_FLAGS=' + ' '.join(ldflags),
+      '-DCMAKE_SHARED_LINKER_FLAGS=' + ' '.join(ldflags),
+      '-DCMAKE_MODULE_LINKER_FLAGS=' + ' '.join(ldflags),
+      '-DCMAKE_INSTALL_PREFIX=' + LLVM_BUILD_DIR,
+      # TODO(thakis): Remove this once official builds pass -Wl,--build-id
+      # explicitly, https://crbug.com/622775
+      '-DENABLE_LINKER_BUILD_ID=ON',
+      '-DCHROMIUM_TOOLS_SRC=%s' % os.path.join(CHROMIUM_DIR, 'tools', 'clang'),
+      '-DCHROMIUM_TOOLS=%s' % ';'.join(args.tools)]
+
+  EnsureDirExists(LLVM_BUILD_DIR)
+  os.chdir(LLVM_BUILD_DIR)
+  RmCmakeCache('.')
+  RunCommand(['cmake'] + cmake_args + [LLVM_DIR],
+             msvc_arch='x64', env=deployment_env)
+
+  if args.gcc_toolchain:
+    # Copy in the right stdlibc++.so.6 so clang can start.
+    if not os.path.exists(os.path.join(LLVM_BUILD_DIR, 'lib')):
+      os.mkdir(os.path.join(LLVM_BUILD_DIR, 'lib'))
+    libstdcpp = subprocess.check_output(
+        [cxx] + cxxflags + ['-print-file-name=libstdc++.so.6']).rstrip()
+    CopyFile(libstdcpp, os.path.join(LLVM_BUILD_DIR, 'lib'))
+
+  RunCommand(['ninja'], msvc_arch='x64')
+
+  if args.tools:
+    # If any Chromium tools were built, install those now.
+    RunCommand(['ninja', 'cr-install'], msvc_arch='x64')
+
+  if sys.platform == 'darwin':
+    # See http://crbug.com/256342
+    RunCommand(['strip', '-x', os.path.join(LLVM_BUILD_DIR, 'bin', 'clang')])
+  elif sys.platform.startswith('linux'):
+    RunCommand(['strip', os.path.join(LLVM_BUILD_DIR, 'bin', 'clang')])
+
+  VeryifyVersionOfBuiltClangMatchesVERSION()
+
+  # Do an out-of-tree build of compiler-rt.
+  # On Windows, this is used to get the 32-bit ASan run-time.
+  # TODO(hans): Remove once the regular build above produces this.
+  # On Mac and Linux, this is used to get the regular 64-bit run-time.
+  # Do a clobbered build due to cmake changes.
+  if os.path.isdir(COMPILER_RT_BUILD_DIR):
+    RmTree(COMPILER_RT_BUILD_DIR)
+  os.makedirs(COMPILER_RT_BUILD_DIR)
+  os.chdir(COMPILER_RT_BUILD_DIR)
+  # TODO(thakis): Add this once compiler-rt can build with clang-cl (see
+  # above).
+  #if args.bootstrap and sys.platform == 'win32':
+    # The bootstrap compiler produces 64-bit binaries by default.
+    #cflags += ['-m32']
+    #cxxflags += ['-m32']
+  compiler_rt_args = base_cmake_args + [
+      '-DCMAKE_C_FLAGS=' + ' '.join(cflags),
+      '-DCMAKE_CXX_FLAGS=' + ' '.join(cxxflags)]
+  if sys.platform == 'darwin':
+    compiler_rt_args += ['-DCOMPILER_RT_ENABLE_IOS=ON']
+  if sys.platform != 'win32':
+    compiler_rt_args += ['-DLLVM_CONFIG_PATH=' +
+                         os.path.join(LLVM_BUILD_DIR, 'bin', 'llvm-config'),
+                        '-DSANITIZER_MIN_OSX_VERSION="10.7"']
+  # compiler-rt is part of the llvm checkout on Windows but a stand-alone
+  # directory elsewhere, see the TODO above COMPILER_RT_DIR.
+  RmCmakeCache('.')
+  RunCommand(['cmake'] + compiler_rt_args +
+             [LLVM_DIR if sys.platform == 'win32' else COMPILER_RT_DIR],
+             msvc_arch='x86', env=deployment_env)
+  RunCommand(['ninja', 'compiler-rt'], msvc_arch='x86')
+
+  # Copy select output to the main tree.
+  # TODO(hans): Make this (and the .gypi and .isolate files) version number
+  # independent.
+  if sys.platform == 'win32':
+    platform = 'windows'
+  elif sys.platform == 'darwin':
+    platform = 'darwin'
+  else:
+    assert sys.platform.startswith('linux')
+    platform = 'linux'
+  asan_rt_lib_src_dir = os.path.join(COMPILER_RT_BUILD_DIR, 'lib', platform)
+  if sys.platform == 'win32':
+    # TODO(thakis): This too is due to compiler-rt being part of the checkout
+    # on Windows, see TODO above COMPILER_RT_DIR.
+    asan_rt_lib_src_dir = os.path.join(COMPILER_RT_BUILD_DIR, 'lib', 'clang',
+                                       VERSION, 'lib', platform)
+  asan_rt_lib_dst_dir = os.path.join(LLVM_BUILD_DIR, 'lib', 'clang',
+                                     VERSION, 'lib', platform)
+  # Blacklists:
+  CopyDirectoryContents(os.path.join(asan_rt_lib_src_dir, '..', '..'),
+                        os.path.join(asan_rt_lib_dst_dir, '..', '..'),
+                        r'^.*blacklist\.txt$')
+  # Headers:
+  if sys.platform != 'win32':
+    CopyDirectoryContents(
+        os.path.join(COMPILER_RT_BUILD_DIR, 'include/sanitizer'),
+        os.path.join(LLVM_BUILD_DIR, 'lib/clang', VERSION, 'include/sanitizer'))
+  # Static and dynamic libraries:
+  CopyDirectoryContents(asan_rt_lib_src_dir, asan_rt_lib_dst_dir)
+  if sys.platform == 'darwin':
+    for dylib in glob.glob(os.path.join(asan_rt_lib_dst_dir, '*.dylib')):
+      # Fix LC_ID_DYLIB for the ASan dynamic libraries to be relative to
+      # @executable_path.
+      # TODO(glider): this is transitional. We'll need to fix the dylib
+      # name either in our build system, or in Clang. See also
+      # http://crbug.com/344836.
+      subprocess.call(['install_name_tool', '-id',
+                       '@executable_path/' + os.path.basename(dylib), dylib])
+
+
+  if sys.platform == 'win32':
+    # Make an extra copy of the sanitizer headers, to be put on the include path
+    # of the fallback compiler.
+    sanitizer_include_dir = os.path.join(LLVM_BUILD_DIR, 'lib', 'clang',
+                                         VERSION, 'include', 'sanitizer')
+    aux_sanitizer_include_dir = os.path.join(LLVM_BUILD_DIR, 'lib', 'clang',
+                                             VERSION, 'include_sanitizer',
+                                             'sanitizer')
+    EnsureDirExists(aux_sanitizer_include_dir)
+    for _, _, files in os.walk(sanitizer_include_dir):
+      for f in files:
+        CopyFile(os.path.join(sanitizer_include_dir, f),
+                 aux_sanitizer_include_dir)
+
+  if args.with_android:
+    make_toolchain = os.path.join(
+        ANDROID_NDK_DIR, 'build', 'tools', 'make_standalone_toolchain.py')
+    for target_arch in ['aarch64', 'arm', 'i686']:
+      # Make standalone Android toolchain for target_arch.
+      toolchain_dir = os.path.join(
+          LLVM_BUILD_DIR, 'android-toolchain-' + target_arch)
+      RunCommand([
+          make_toolchain,
+          '--api=' + ('21' if target_arch == 'aarch64' else '19'),
+          '--force',
+          '--install-dir=%s' % toolchain_dir,
+          '--stl=stlport',
+          '--arch=' + {
+              'aarch64': 'arm64',
+              'arm': 'arm',
+              'i686': 'x86',
+          }[target_arch]])
+      # Android NDK r9d copies a broken unwind.h into the toolchain, see
+      # http://crbug.com/357890
+      for f in glob.glob(os.path.join(toolchain_dir, 'include/c++/*/unwind.h')):
+        os.remove(f)
+
+      # Build ASan runtime for Android in a separate build tree.
+      build_dir = os.path.join(LLVM_BUILD_DIR, 'android-' + target_arch)
+      if not os.path.exists(build_dir):
+        os.mkdir(os.path.join(build_dir))
+      os.chdir(build_dir)
+      cflags = ['--target=%s-linux-androideabi' % target_arch,
+                '--sysroot=%s/sysroot' % toolchain_dir,
+                '-B%s' % toolchain_dir]
+      android_args = base_cmake_args + [
+        '-DCMAKE_C_COMPILER=' + os.path.join(LLVM_BUILD_DIR, 'bin/clang'),
+        '-DCMAKE_CXX_COMPILER=' + os.path.join(LLVM_BUILD_DIR, 'bin/clang++'),
+        '-DLLVM_CONFIG_PATH=' + os.path.join(LLVM_BUILD_DIR, 'bin/llvm-config'),
+        '-DCMAKE_C_FLAGS=' + ' '.join(cflags),
+        '-DCMAKE_CXX_FLAGS=' + ' '.join(cflags),
+        '-DANDROID=1']
+      RmCmakeCache('.')
+      RunCommand(['cmake'] + android_args + [COMPILER_RT_DIR])
+      RunCommand(['ninja', 'libclang_rt.asan-%s-android.so' % target_arch])
+
+      # And copy it into the main build tree.
+      runtime = 'libclang_rt.asan-%s-android.so' % target_arch
+      for root, _, files in os.walk(build_dir):
+        if runtime in files:
+          shutil.copy(os.path.join(root, runtime), asan_rt_lib_dst_dir)
+
+  # Run tests.
+  if args.run_tests or use_head_revision:
+    os.chdir(LLVM_BUILD_DIR)
+    RunCommand(['ninja', 'cr-check-all'], msvc_arch='x64')
+  if args.run_tests:
+    if sys.platform == 'win32':
+      CopyDiaDllTo(os.path.join(LLVM_BUILD_DIR, 'bin'))
+    os.chdir(LLVM_BUILD_DIR)
+    RunCommand(['ninja', 'check-all'], msvc_arch='x64')
+
+  WriteStampFile(PACKAGE_VERSION)
+  print 'Clang update was successful.'
+  return 0
+
+
+def main():
+  parser = argparse.ArgumentParser(description='Build Clang.')
+  parser.add_argument('--bootstrap', action='store_true',
+                      help='first build clang with CC, then with itself.')
+  parser.add_argument('--if-needed', action='store_true',
+                      help="run only if the script thinks clang is needed")
+  parser.add_argument('--force-local-build', action='store_true',
+                      help="don't try to download prebuild binaries")
+  parser.add_argument('--gcc-toolchain', help='set the version for which gcc '
+                      'version be used for building; --gcc-toolchain=/opt/foo '
+                      'picks /opt/foo/bin/gcc')
+  parser.add_argument('--lto-gold-plugin', action='store_true',
+                      help='build LLVM Gold plugin with LTO')
+  parser.add_argument('--llvm-force-head-revision', action='store_true',
+                      help=('use the revision in the repo when printing '
+                            'the revision'))
+  parser.add_argument('--print-revision', action='store_true',
+                      help='print current clang revision and exit.')
+  parser.add_argument('--print-clang-version', action='store_true',
+                      help='print current clang version (e.g. x.y.z) and exit.')
+  parser.add_argument('--run-tests', action='store_true',
+                      help='run tests after building; only for local builds')
+  parser.add_argument('--tools', nargs='*',
+                      help='select which chrome tools to build',
+                      default=['plugins', 'blink_gc_plugin'])
+  parser.add_argument('--without-android', action='store_false',
+                      help='don\'t build Android ASan runtime (linux only)',
+                      dest='with_android',
+                      default=sys.platform.startswith('linux'))
+  args = parser.parse_args()
+
+  if args.lto_gold_plugin and not args.bootstrap:
+    print '--lto-gold-plugin requires --bootstrap'
+    return 1
+  if args.lto_gold_plugin and not sys.platform.startswith('linux'):
+    print '--lto-gold-plugin is only effective on Linux. Ignoring the option.'
+    args.lto_gold_plugin = False
+
+  if args.if_needed:
+    is_clang_required = False
+    # clang is always used on Mac and Linux.
+    if sys.platform == 'darwin' or sys.platform.startswith('linux'):
+      is_clang_required = True
+    # clang requested via $GYP_DEFINES.
+    if re.search(r'\b(clang|asan|lsan|msan|tsan)=1',
+                 os.environ.get('GYP_DEFINES', '')):
+      is_clang_required = True
+    # clang previously downloaded, keep it up to date.
+    # If you don't want this, delete third_party/llvm-build on your machine.
+    if os.path.isdir(LLVM_BUILD_DIR):
+      is_clang_required = True
+    if not is_clang_required:
+      return 0
+    if re.search(r'\b(make_clang_dir)=', os.environ.get('GYP_DEFINES', '')):
+      print 'Skipping Clang update (make_clang_dir= was set in GYP_DEFINES).'
+      return 0
+
+  global CLANG_REVISION, PACKAGE_VERSION
+  if args.print_revision:
+    if use_head_revision or args.llvm_force_head_revision:
+      print GetSvnRevision(LLVM_DIR)
+    else:
+      print PACKAGE_VERSION
+    return 0
+
+  if args.print_clang_version:
+    sys.stdout.write(VERSION)
+    return 0
+
+  # Don't buffer stdout, so that print statements are immediately flushed.
+  # Do this only after --print-revision has been handled, else we'll get
+  # an error message when this script is run from gn for some reason.
+  sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)
+
+  if use_head_revision:
+    # Use a real revision number rather than HEAD to make sure that the stamp
+    # file logic works.
+    CLANG_REVISION = GetSvnRevision(LLVM_REPO_URL)
+    PACKAGE_VERSION = CLANG_REVISION + '-0'
+
+    args.force_local_build = True
+    if 'OS=android' not in os.environ.get('GYP_DEFINES', ''):
+      # Only build the Android ASan rt on ToT bots when targetting Android.
+      args.with_android = False
+
+  return UpdateClang(args)
+
+
+if __name__ == '__main__':
+  sys.exit(main())
diff --git a/tools/clang/scripts/update.sh b/tools/clang/scripts/update.sh
new file mode 100755
index 00000000000..d85deae23c3
--- /dev/null
+++ b/tools/clang/scripts/update.sh
@@ -0,0 +1,724 @@
+#!/usr/bin/env bash
+# Copyright (c) 2012 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# This script will check out llvm and clang into third_party/llvm and build it.
+
+# Do NOT CHANGE this if you don't know what you're doing -- see
+# https://code.google.com/p/chromium/wiki/UpdatingClang
+# Reverting problematic clang rolls is safe, though.
+CLANG_REVISION=241602
+
+# This is incremented when pushing a new build of Clang at the same revision.
+CLANG_SUB_REVISION=3
+
+PACKAGE_VERSION="${CLANG_REVISION}-${CLANG_SUB_REVISION}"
+
+THIS_DIR="$(dirname "${0}")"
+LLVM_DIR="${THIS_DIR}/../../../third_party/llvm"
+LLVM_BUILD_DIR="${LLVM_DIR}/../llvm-build/Release+Asserts"
+COMPILER_RT_BUILD_DIR="${LLVM_DIR}/../llvm-build/compiler-rt"
+LLVM_BOOTSTRAP_DIR="${LLVM_DIR}/../llvm-bootstrap"
+LLVM_BOOTSTRAP_INSTALL_DIR="${LLVM_DIR}/../llvm-bootstrap-install"
+CLANG_DIR="${LLVM_DIR}/tools/clang"
+COMPILER_RT_DIR="${LLVM_DIR}/compiler-rt"
+LIBCXX_DIR="${LLVM_DIR}/projects/libcxx"
+LIBCXXABI_DIR="${LLVM_DIR}/projects/libcxxabi"
+ANDROID_NDK_DIR="${THIS_DIR}/../../../third_party/android_tools/ndk"
+STAMP_FILE="${LLVM_DIR}/../llvm-build/cr_build_revision"
+CHROMIUM_TOOLS_DIR="${THIS_DIR}/.."
+BINUTILS_DIR="${THIS_DIR}/../../../third_party/binutils"
+
+ABS_CHROMIUM_TOOLS_DIR="${PWD}/${CHROMIUM_TOOLS_DIR}"
+ABS_LIBCXX_DIR="${PWD}/${LIBCXX_DIR}"
+ABS_LIBCXXABI_DIR="${PWD}/${LIBCXXABI_DIR}"
+ABS_LLVM_DIR="${PWD}/${LLVM_DIR}"
+ABS_LLVM_BUILD_DIR="${PWD}/${LLVM_BUILD_DIR}"
+ABS_COMPILER_RT_DIR="${PWD}/${COMPILER_RT_DIR}"
+ABS_BINUTILS_DIR="${PWD}/${BINUTILS_DIR}"
+
+# ${A:-a} returns $A if it's set, a else.
+LLVM_REPO_URL=${LLVM_URL:-https://llvm.org/svn/llvm-project}
+
+CDS_URL=https://commondatastorage.googleapis.com/chromium-browser-clang
+
+if [[ -z "$GYP_DEFINES" ]]; then
+  GYP_DEFINES=
+fi
+if [[ -z "$GYP_GENERATORS" ]]; then
+  GYP_GENERATORS=
+fi
+if [[ -z "$LLVM_DOWNLOAD_GOLD_PLUGIN" ]]; then
+  LLVM_DOWNLOAD_GOLD_PLUGIN=
+fi
+
+
+# Die if any command dies, error on undefined variable expansions.
+set -eu
+
+
+if [[ -n ${LLVM_FORCE_HEAD_REVISION:-''} ]]; then
+  # Use a real revision number rather than HEAD to make sure that the stamp file
+  # logic works.
+  CLANG_REVISION=$(svn info "$LLVM_REPO_URL" \
+      | grep 'Revision:' | awk '{ printf $2; }')
+  PACKAGE_VERSION="${CLANG_REVISION}-0"
+fi
+
+OS="$(uname -s)"
+
+# Parse command line options.
+if_needed=
+force_local_build=
+run_tests=
+bootstrap=
+with_android=yes
+chrome_tools="plugins;blink_gc_plugin"
+gcc_toolchain=
+with_patches=yes
+
+if [[ "${OS}" = "Darwin" ]]; then
+  with_android=
+fi
+
+while [[ $# > 0 ]]; do
+  case $1 in
+    --bootstrap)
+      bootstrap=yes
+      ;;
+    --if-needed)
+      if_needed=yes
+      ;;
+    --force-local-build)
+      force_local_build=yes
+      ;;
+    --print-revision)
+      if [[ -n ${LLVM_FORCE_HEAD_REVISION:-''} ]]; then
+        svn info "$LLVM_DIR" | grep 'Revision:' | awk '{ printf $2; }'
+      else
+        echo $PACKAGE_VERSION
+      fi
+      exit 0
+      ;;
+    --run-tests)
+      run_tests=yes
+      ;;
+    --without-android)
+      with_android=
+      ;;
+    --without-patches)
+      with_patches=
+      ;;
+    --with-chrome-tools)
+      shift
+      if [[ $# == 0 ]]; then
+        echo "--with-chrome-tools requires an argument."
+        exit 1
+      fi
+      chrome_tools=$1
+      ;;
+    --gcc-toolchain)
+      shift
+      if [[ $# == 0 ]]; then
+        echo "--gcc-toolchain requires an argument."
+        exit 1
+      fi
+      if [[ -x "$1/bin/gcc" ]]; then
+        gcc_toolchain=$1
+      else
+        echo "Invalid --gcc-toolchain: '$1'."
+        echo "'$1/bin/gcc' does not appear to be valid."
+        exit 1
+      fi
+      ;;
+
+    --help)
+      echo "usage: $0 [--force-local-build] [--if-needed] [--run-tests] "
+      echo "--bootstrap: First build clang with CC, then with itself."
+      echo "--force-local-build: Don't try to download prebuilt binaries."
+      echo "--if-needed: Download clang only if the script thinks it is needed."
+      echo "--run-tests: Run tests after building. Only for local builds."
+      echo "--print-revision: Print current clang revision and exit."
+      echo "--without-android: Don't build ASan Android runtime library."
+      echo "--with-chrome-tools: Select which chrome tools to build." \
+           "Defaults to plugins;blink_gc_plugin."
+      echo "    Example: --with-chrome-tools plugins;empty-string"
+      echo "--gcc-toolchain: Set the prefix for which GCC version should"
+      echo "    be used for building. For example, to use gcc in"
+      echo "    /opt/foo/bin/gcc, use '--gcc-toolchain '/opt/foo"
+      echo "--without-patches: Don't apply local patches."
+      echo
+      exit 1
+      ;;
+    *)
+      echo "Unknown argument: '$1'."
+      echo "Use --help for help."
+      exit 1
+      ;;
+  esac
+  shift
+done
+
+if [[ -n ${LLVM_FORCE_HEAD_REVISION:-''} ]]; then
+  force_local_build=yes
+
+  # Skip local patches when using HEAD: they probably don't apply anymore.
+  with_patches=
+
+  if ! [[ "$GYP_DEFINES" =~ .*OS=android.* ]]; then
+    # Only build the Android ASan rt when targetting Android.
+    with_android=
+  fi
+
+  LLVM_BUILD_TOOLS_DIR="${ABS_LLVM_DIR}/../llvm-build-tools"
+
+  if [[ "${OS}" == "Linux" ]] && [[ -z "${gcc_toolchain}" ]]; then
+    if [[ $(gcc -dumpversion) < "4.7.0" ]]; then
+      # We need a newer GCC version.
+      if [[ ! -e "${LLVM_BUILD_TOOLS_DIR}/gcc482" ]]; then
+        echo "Downloading pre-built GCC 4.8.2..."
+        mkdir -p "${LLVM_BUILD_TOOLS_DIR}"
+        curl --fail -L "${CDS_URL}/tools/gcc482.tgz" | \
+          tar zxf - -C "${LLVM_BUILD_TOOLS_DIR}"
+        echo Done
+      fi
+      gcc_toolchain="${LLVM_BUILD_TOOLS_DIR}/gcc482"
+    else
+      # Always set gcc_toolchain; llvm-symbolizer needs the bundled libstdc++.
+      gcc_toolchain="$(dirname $(dirname $(which gcc)))"
+    fi
+  fi
+
+  if [[ "${OS}" == "Linux" || "${OS}" == "Darwin" ]]; then
+    if [[ $(cmake --version | grep -Eo '[0-9.]+') < "3.0" ]]; then
+      # We need a newer CMake version.
+      if [[ ! -e "${LLVM_BUILD_TOOLS_DIR}/cmake310" ]]; then
+        echo "Downloading pre-built CMake 3.10..."
+        mkdir -p "${LLVM_BUILD_TOOLS_DIR}"
+        curl --fail -L "${CDS_URL}/tools/cmake310_${OS}.tgz" | \
+          tar zxf - -C "${LLVM_BUILD_TOOLS_DIR}"
+        echo Done
+      fi
+      export PATH="${LLVM_BUILD_TOOLS_DIR}/cmake310/bin:${PATH}"
+    fi
+  fi
+
+  echo "LLVM_FORCE_HEAD_REVISION was set; using r${CLANG_REVISION}"
+fi
+
+if [[ -n "$if_needed" ]]; then
+  if [[ "${OS}" == "Darwin" ]]; then
+    # clang is always used on Mac.
+    true
+  elif [[ "${OS}" == "Linux" ]]; then
+    # clang is also aways used on Linux.
+    true
+  elif [[ "$GYP_DEFINES" =~ .*(clang|tsan|asan|lsan|msan)=1.* ]]; then
+    # clang requested via $GYP_DEFINES.
+    true
+  elif [[ -d "${LLVM_BUILD_DIR}" ]]; then
+    # clang previously downloaded, keep it up-to-date.
+    # If you don't want this, delete third_party/llvm-build on your machine.
+    true
+  else
+    # clang wasn't needed, not doing anything.
+    exit 0
+  fi
+fi
+
+
+# Check if there's anything to be done, exit early if not.
+if [[ -f "${STAMP_FILE}" ]]; then
+  PREVIOUSLY_BUILT_REVISON=$(cat "${STAMP_FILE}")
+  if [[ -z "$force_local_build" ]] && \
+       [[ "${PREVIOUSLY_BUILT_REVISON}" = \
+          "${PACKAGE_VERSION}" ]]; then
+    echo "Clang already at ${PACKAGE_VERSION}"
+    exit 0
+  fi
+fi
+# To always force a new build if someone interrupts their build half way.
+rm -f "${STAMP_FILE}"
+
+
+if [[ -z "$force_local_build" ]]; then
+  # Check if there's a prebuilt binary and if so just fetch that. That's faster,
+  # and goma relies on having matching binary hashes on client and server too.
+  CDS_FILE="clang-${PACKAGE_VERSION}.tgz"
+  CDS_OUT_DIR=$(mktemp -d -t clang_download.XXXXXX)
+  CDS_OUTPUT="${CDS_OUT_DIR}/${CDS_FILE}"
+  if [ "${OS}" = "Linux" ]; then
+    CDS_FULL_URL="${CDS_URL}/Linux_x64/${CDS_FILE}"
+  elif [ "${OS}" = "Darwin" ]; then
+    CDS_FULL_URL="${CDS_URL}/Mac/${CDS_FILE}"
+  fi
+  echo Trying to download prebuilt clang
+  if which curl > /dev/null; then
+    curl -L --fail "${CDS_FULL_URL}" -o "${CDS_OUTPUT}" || \
+        rm -rf "${CDS_OUT_DIR}"
+  elif which wget > /dev/null; then
+    wget "${CDS_FULL_URL}" -O "${CDS_OUTPUT}" || rm -rf "${CDS_OUT_DIR}"
+  else
+    echo "Neither curl nor wget found. Please install one of these."
+    exit 1
+  fi
+  if [ -f "${CDS_OUTPUT}" ]; then
+    rm -rf "${LLVM_BUILD_DIR}"
+    mkdir -p "${LLVM_BUILD_DIR}"
+    tar -xzf "${CDS_OUTPUT}" -C "${LLVM_BUILD_DIR}"
+    echo clang "${PACKAGE_VERSION}" unpacked
+    echo "${PACKAGE_VERSION}" > "${STAMP_FILE}"
+    rm -rf "${CDS_OUT_DIR}"
+    # Download the gold plugin if requested to by an environment variable.
+    # This is used by the CFI ClusterFuzz bot.
+    if [[ -n "${LLVM_DOWNLOAD_GOLD_PLUGIN}" ]]; then
+      ${THIS_DIR}/../../../build/download_gold_plugin.py
+    fi
+    exit 0
+  else
+    echo Did not find prebuilt clang "${PACKAGE_VERSION}", building
+  fi
+fi
+
+if [[ -n "${with_android}" ]] && ! [[ -d "${ANDROID_NDK_DIR}" ]]; then
+  echo "Android NDK not found at ${ANDROID_NDK_DIR}"
+  echo "The Android NDK is needed to build a Clang whose -fsanitize=address"
+  echo "works on Android. See "
+  echo "http://code.google.com/p/chromium/wiki/AndroidBuildInstructions for how"
+  echo "to install the NDK, or pass --without-android."
+  exit 1
+fi
+
+# Check that cmake and ninja are available.
+if ! which cmake > /dev/null; then
+  echo "CMake needed to build clang; please install"
+  exit 1
+fi
+if ! which ninja > /dev/null; then
+  echo "ninja needed to build clang, please install"
+  exit 1
+fi
+
+echo Reverting previously patched files
+for i in \
+      "${CLANG_DIR}/test/Index/crash-recovery-modules.m" \
+      "${CLANG_DIR}/unittests/libclang/LibclangTest.cpp" \
+      "${COMPILER_RT_DIR}/lib/asan/asan_rtl.cc" \
+      "${COMPILER_RT_DIR}/test/asan/TestCases/Linux/new_array_cookie_test.cc" \
+      "${LLVM_DIR}/test/DebugInfo/gmlt.ll" \
+      "${LLVM_DIR}/lib/CodeGen/SpillPlacement.cpp" \
+      "${LLVM_DIR}/lib/CodeGen/SpillPlacement.h" \
+      "${LLVM_DIR}/lib/Transforms/Instrumentation/MemorySanitizer.cpp" \
+      "${CLANG_DIR}/test/Driver/env.c" \
+      "${CLANG_DIR}/lib/Frontend/InitPreprocessor.cpp" \
+      "${CLANG_DIR}/test/Frontend/exceptions.c" \
+      "${CLANG_DIR}/test/Preprocessor/predefined-exceptions.m" \
+      "${LLVM_DIR}/test/Bindings/Go/go.test" \
+      "${CLANG_DIR}/lib/Parse/ParseExpr.cpp" \
+      "${CLANG_DIR}/lib/Parse/ParseTemplate.cpp" \
+      "${CLANG_DIR}/lib/Sema/SemaDeclCXX.cpp" \
+      "${CLANG_DIR}/lib/Sema/SemaExprCXX.cpp" \
+      "${CLANG_DIR}/test/SemaCXX/default2.cpp" \
+      "${CLANG_DIR}/test/SemaCXX/typo-correction-delayed.cpp" \
+      "${COMPILER_RT_DIR}/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc" \
+      "${COMPILER_RT_DIR}/test/tsan/signal_segv_handler.cc" \
+      "${COMPILER_RT_DIR}/lib/sanitizer_common/sanitizer_coverage_libcdep.cc" \
+      "${COMPILER_RT_DIR}/cmake/config-ix.cmake" \
+      "${COMPILER_RT_DIR}/CMakeLists.txt" \
+      "${COMPILER_RT_DIR}/lib/ubsan/ubsan_platform.h" \
+      ; do
+  if [[ -e "${i}" ]]; then
+    rm -f "${i}"  # For unversioned files.
+    svn revert "${i}"
+  fi;
+done
+
+echo Remove the Clang tools shim dir
+CHROME_TOOLS_SHIM_DIR=${ABS_LLVM_DIR}/tools/chrometools
+rm -rfv ${CHROME_TOOLS_SHIM_DIR}
+
+echo Getting LLVM r"${CLANG_REVISION}" in "${LLVM_DIR}"
+if ! svn co --force "${LLVM_REPO_URL}/llvm/trunk@${CLANG_REVISION}" \
+                    "${LLVM_DIR}"; then
+  echo Checkout failed, retrying
+  rm -rf "${LLVM_DIR}"
+  svn co --force "${LLVM_REPO_URL}/llvm/trunk@${CLANG_REVISION}" "${LLVM_DIR}"
+fi
+
+echo Getting clang r"${CLANG_REVISION}" in "${CLANG_DIR}"
+svn co --force "${LLVM_REPO_URL}/cfe/trunk@${CLANG_REVISION}" "${CLANG_DIR}"
+
+# We have moved from building compiler-rt in the LLVM tree, to a separate
+# directory. Nuke any previous checkout to avoid building it.
+rm -rf "${LLVM_DIR}/projects/compiler-rt"
+
+echo Getting compiler-rt r"${CLANG_REVISION}" in "${COMPILER_RT_DIR}"
+svn co --force "${LLVM_REPO_URL}/compiler-rt/trunk@${CLANG_REVISION}" \
+               "${COMPILER_RT_DIR}"
+
+# clang needs a libc++ checkout, else -stdlib=libc++ won't find includes
+# (i.e. this is needed for bootstrap builds).
+if [ "${OS}" = "Darwin" ]; then
+  echo Getting libc++ r"${CLANG_REVISION}" in "${LIBCXX_DIR}"
+  svn co --force "${LLVM_REPO_URL}/libcxx/trunk@${CLANG_REVISION}" \
+                 "${LIBCXX_DIR}"
+fi
+
+# While we're bundling our own libc++ on OS X, we need to compile libc++abi
+# into it too (since OS X 10.6 doesn't have libc++abi.dylib either).
+if [ "${OS}" = "Darwin" ]; then
+  echo Getting libc++abi r"${CLANG_REVISION}" in "${LIBCXXABI_DIR}"
+  svn co --force "${LLVM_REPO_URL}/libcxxabi/trunk@${CLANG_REVISION}" \
+                 "${LIBCXXABI_DIR}"
+fi
+
+if [[ -n "$with_patches" ]]; then
+
+  # Apply patch for tests failing with --disable-pthreads (llvm.org/PR11974)
+  pushd "${CLANG_DIR}"
+  cat << 'EOF' |
+--- test/Index/crash-recovery-modules.m	(revision 202554)
++++ test/Index/crash-recovery-modules.m	(working copy)
+@@ -12,6 +12,8 @@
+ 
+ // REQUIRES: crash-recovery
+ // REQUIRES: shell
++// XFAIL: *
++//    (PR11974)
+ 
+ @import Crash;
+EOF
+patch -p0
+popd
+
+pushd "${CLANG_DIR}"
+cat << 'EOF' |
+--- unittests/libclang/LibclangTest.cpp (revision 215949)
++++ unittests/libclang/LibclangTest.cpp (working copy)
+@@ -431,7 +431,7 @@
+   EXPECT_EQ(0U, clang_getNumDiagnostics(ClangTU));
+ }
+
+-TEST_F(LibclangReparseTest, ReparseWithModule) {
++TEST_F(LibclangReparseTest, DISABLED_ReparseWithModule) {
+   const char *HeaderTop = "#ifndef H\n#define H\nstruct Foo { int bar;";
+   const char *HeaderBottom = "\n};\n#endif\n";
+   const char *MFile = "#include \"HeaderFile.h\"\nint main() {"
+EOF
+  patch -p0
+  popd
+
+  # This Go bindings test doesn't work after the bootstrap build on Linux. (PR21552)
+  pushd "${LLVM_DIR}"
+  cat << 'EOF' |
+--- test/Bindings/Go/go.test    (revision 223109)
++++ test/Bindings/Go/go.test    (working copy)
+@@ -1,3 +1,3 @@
+-; RUN: llvm-go test llvm.org/llvm/bindings/go/llvm
++; RUN: true
+ 
+ ; REQUIRES: shell
+EOF
+  patch -p0
+  popd
+
+  # The UBSan run-time, which is now bundled with the ASan run-time, doesn't work
+  # on Mac OS X 10.8 (PR23539).
+  pushd "${COMPILER_RT_DIR}"
+  cat << 'EOF' |
+Index: CMakeLists.txt
+===================================================================
+--- CMakeLists.txt	(revision 241602)
++++ CMakeLists.txt	(working copy)
+@@ -305,6 +305,7 @@
+       list(APPEND SANITIZER_COMMON_SUPPORTED_OS iossim)
+     endif()
+   endif()
++  set(SANITIZER_MIN_OSX_VERSION "10.7")
+   if(SANITIZER_MIN_OSX_VERSION VERSION_LESS "10.7")
+     message(FATAL_ERROR "Too old OS X version: ${SANITIZER_MIN_OSX_VERSION}")
+   endif()
+EOF
+  patch -p0
+  popd
+
+fi
+
+# Echo all commands.
+set -x
+
+# Set default values for CC and CXX if they're not set in the environment.
+CC=${CC:-cc}
+CXX=${CXX:-c++}
+
+if [[ -n "${gcc_toolchain}" ]]; then
+  # Use the specified gcc installation for building.
+  CC="$gcc_toolchain/bin/gcc"
+  CXX="$gcc_toolchain/bin/g++"
+  # Set LD_LIBRARY_PATH to make auxiliary targets (tablegen, bootstrap compiler,
+  # etc.) find the .so.
+  export LD_LIBRARY_PATH="$(dirname $(${CXX} -print-file-name=libstdc++.so.6))"
+fi
+
+CFLAGS=""
+CXXFLAGS=""
+LDFLAGS=""
+
+# LLVM uses C++11 starting in llvm 3.5. On Linux, this means libstdc++4.7+ is
+# needed, on OS X it requires libc++. clang only automatically links to libc++
+# when targeting OS X 10.9+, so add stdlib=libc++ explicitly so clang can run on
+# OS X versions as old as 10.7.
+# TODO(thakis): Some bots are still on 10.6 (nacl...), so for now bundle
+# libc++.dylib.  Remove this once all bots are on 10.7+, then use
+# -DLLVM_ENABLE_LIBCXX=ON and change deployment_target to 10.7.
+deployment_target=""
+
+if [ "${OS}" = "Darwin" ]; then
+  # When building on 10.9, /usr/include usually doesn't exist, and while
+  # Xcode's clang automatically sets a sysroot, self-built clangs don't.
+  CFLAGS="-isysroot $(xcrun --show-sdk-path)"
+  CXXFLAGS="-stdlib=libc++ -nostdinc++ -I${ABS_LIBCXX_DIR}/include ${CFLAGS}"
+
+  if [[ -n "${bootstrap}" ]]; then
+    deployment_target=10.6
+  fi
+fi
+
+# Build bootstrap clang if requested.
+if [[ -n "${bootstrap}" ]]; then
+  ABS_INSTALL_DIR="${PWD}/${LLVM_BOOTSTRAP_INSTALL_DIR}"
+  echo "Building bootstrap compiler"
+  mkdir -p "${LLVM_BOOTSTRAP_DIR}"
+  pushd "${LLVM_BOOTSTRAP_DIR}"
+
+  cmake -GNinja \
+      -DCMAKE_BUILD_TYPE=Release \
+      -DLLVM_ENABLE_ASSERTIONS=ON \
+      -DLLVM_TARGETS_TO_BUILD=host \
+      -DLLVM_ENABLE_THREADS=OFF \
+      -DCMAKE_INSTALL_PREFIX="${ABS_INSTALL_DIR}" \
+      -DCMAKE_C_COMPILER="${CC}" \
+      -DCMAKE_CXX_COMPILER="${CXX}" \
+      -DCMAKE_C_FLAGS="${CFLAGS}" \
+      -DCMAKE_CXX_FLAGS="${CXXFLAGS}" \
+      ../llvm
+
+  ninja
+  if [[ -n "${run_tests}" ]]; then
+    ninja check-all
+  fi
+
+  ninja install
+  if [[ -n "${gcc_toolchain}" ]]; then
+    # Copy that gcc's stdlibc++.so.6 to the build dir, so the bootstrap
+    # compiler can start.
+    cp -v "$(${CXX} -print-file-name=libstdc++.so.6)" \
+      "${ABS_INSTALL_DIR}/lib/"
+  fi
+
+  popd
+  CC="${ABS_INSTALL_DIR}/bin/clang"
+  CXX="${ABS_INSTALL_DIR}/bin/clang++"
+
+  if [[ -n "${gcc_toolchain}" ]]; then
+    # Tell the bootstrap compiler to use a specific gcc prefix to search
+    # for standard library headers and shared object file.
+    CFLAGS="--gcc-toolchain=${gcc_toolchain}"
+    CXXFLAGS="--gcc-toolchain=${gcc_toolchain}"
+  fi
+
+  echo "Building final compiler"
+fi
+
+# Build clang (in a separate directory).
+# The clang bots have this path hardcoded in built/scripts/slave/compile.py,
+# so if you change it you also need to change these links.
+mkdir -p "${LLVM_BUILD_DIR}"
+pushd "${LLVM_BUILD_DIR}"
+
+# Build libc++.dylib while some bots are still on OS X 10.6.
+if [ "${OS}" = "Darwin" ]; then
+  rm -rf libcxxbuild
+  LIBCXXFLAGS="-O3 -std=c++11 -fstrict-aliasing"
+
+  # libcxx and libcxxabi both have a file stdexcept.cpp, so put their .o files
+  # into different subdirectories.
+  mkdir -p libcxxbuild/libcxx
+  pushd libcxxbuild/libcxx
+  ${CXX:-c++} -c ${CXXFLAGS} ${LIBCXXFLAGS} "${ABS_LIBCXX_DIR}"/src/*.cpp
+  popd
+
+  mkdir -p libcxxbuild/libcxxabi
+  pushd libcxxbuild/libcxxabi
+  ${CXX:-c++} -c ${CXXFLAGS} ${LIBCXXFLAGS} "${ABS_LIBCXXABI_DIR}"/src/*.cpp -I"${ABS_LIBCXXABI_DIR}/include"
+  popd
+
+  pushd libcxxbuild
+  ${CC:-cc} libcxx/*.o libcxxabi/*.o -o libc++.1.dylib -dynamiclib \
+    -nodefaultlibs -current_version 1 -compatibility_version 1 \
+    -lSystem -install_name @executable_path/libc++.dylib \
+    -Wl,-unexported_symbols_list,${ABS_LIBCXX_DIR}/lib/libc++unexp.exp \
+    -Wl,-force_symbols_not_weak_list,${ABS_LIBCXX_DIR}/lib/notweak.exp \
+    -Wl,-force_symbols_weak_list,${ABS_LIBCXX_DIR}/lib/weak.exp
+  ln -sf libc++.1.dylib libc++.dylib
+  popd
+  LDFLAGS+="-stdlib=libc++ -L${PWD}/libcxxbuild"
+
+  if [[ -n "${bootstrap}" ]]; then
+    # Now that the libc++ headers have been installed and libc++.dylib is built,
+    # delete the libc++ checkout again so that it's not part of the main
+    # build below -- the libc++(abi) tests don't pass on OS X in bootstrap
+    # builds (http://llvm.org/PR24068)
+    rm -rf "${ABS_LIBCXX_DIR}"
+    rm -rf "${ABS_LIBCXXABI_DIR}"
+    CXXFLAGS="-stdlib=libc++ -nostdinc++ -I${ABS_INSTALL_DIR}/include/c++/v1 ${CFLAGS}"
+  fi
+fi
+
+# Find the binutils include dir for the gold plugin.
+BINUTILS_INCDIR=""
+if [ "${OS}" = "Linux" ]; then
+  BINUTILS_INCDIR="${ABS_BINUTILS_DIR}/Linux_x64/Release/include"
+fi
+
+
+# If building at head, define a macro that plugins can use for #ifdefing
+# out code that builds at head, but not at CLANG_REVISION or vice versa.
+if [[ -n ${LLVM_FORCE_HEAD_REVISION:-''} ]]; then
+  CFLAGS="${CFLAGS} -DLLVM_FORCE_HEAD_REVISION"
+  CXXFLAGS="${CXXFLAGS} -DLLVM_FORCE_HEAD_REVISION"
+fi
+
+# Hook the Chromium tools into the LLVM build. Several Chromium tools have
+# dependencies on LLVM/Clang libraries. The LLVM build detects implicit tools
+# in the tools subdirectory, so install a shim CMakeLists.txt that forwards to
+# the real directory for the Chromium tools.
+# Note that the shim directory name intentionally has no _ or _. The implicit
+# tool detection logic munges them in a weird way.
+mkdir -v ${CHROME_TOOLS_SHIM_DIR}
+cat > ${CHROME_TOOLS_SHIM_DIR}/CMakeLists.txt << EOF
+# Since tools/clang isn't actually a subdirectory, use the two argument version
+# to specify where build artifacts go. CMake doesn't allow reusing the same
+# binary dir for multiple source dirs, so the build artifacts have to go into a
+# subdirectory...
+add_subdirectory(\${CHROMIUM_TOOLS_SRC} \${CMAKE_CURRENT_BINARY_DIR}/a)
+EOF
+rm -fv CMakeCache.txt
+MACOSX_DEPLOYMENT_TARGET=${deployment_target} cmake -GNinja \
+    -DCMAKE_BUILD_TYPE=Release \
+    -DLLVM_ENABLE_ASSERTIONS=ON \
+    -DLLVM_ENABLE_THREADS=OFF \
+    -DLLVM_BINUTILS_INCDIR="${BINUTILS_INCDIR}" \
+    -DCMAKE_C_COMPILER="${CC}" \
+    -DCMAKE_CXX_COMPILER="${CXX}" \
+    -DCMAKE_C_FLAGS="${CFLAGS}" \
+    -DCMAKE_CXX_FLAGS="${CXXFLAGS}" \
+    -DCMAKE_EXE_LINKER_FLAGS="${LDFLAGS}" \
+    -DCMAKE_SHARED_LINKER_FLAGS="${LDFLAGS}" \
+    -DCMAKE_MODULE_LINKER_FLAGS="${LDFLAGS}" \
+    -DCMAKE_INSTALL_PREFIX="${ABS_LLVM_BUILD_DIR}" \
+    -DCHROMIUM_TOOLS_SRC="${ABS_CHROMIUM_TOOLS_DIR}" \
+    -DCHROMIUM_TOOLS="${chrome_tools}" \
+    "${ABS_LLVM_DIR}"
+env
+
+if [[ -n "${gcc_toolchain}" ]]; then
+  # Copy in the right stdlibc++.so.6 so clang can start.
+  mkdir -p lib
+  cp -v "$(${CXX} ${CXXFLAGS} -print-file-name=libstdc++.so.6)" lib/
+fi
+
+ninja
+# If any Chromium tools were built, install those now.
+if [[ -n "${chrome_tools}" ]]; then
+  ninja cr-install
+fi
+
+STRIP_FLAGS=
+if [ "${OS}" = "Darwin" ]; then
+  # See http://crbug.com/256342
+  STRIP_FLAGS=-x
+
+  cp libcxxbuild/libc++.1.dylib bin/
+fi
+strip ${STRIP_FLAGS} bin/clang
+popd
+
+# Build compiler-rt out-of-tree.
+mkdir -p "${COMPILER_RT_BUILD_DIR}"
+pushd "${COMPILER_RT_BUILD_DIR}"
+
+rm -fv CMakeCache.txt
+MACOSX_DEPLOYMENT_TARGET=${deployment_target} cmake -GNinja \
+    -DCMAKE_BUILD_TYPE=Release \
+    -DLLVM_ENABLE_ASSERTIONS=ON \
+    -DLLVM_ENABLE_THREADS=OFF \
+    -DCMAKE_C_COMPILER="${CC}" \
+    -DCMAKE_CXX_COMPILER="${CXX}" \
+    -DLLVM_CONFIG_PATH="${ABS_LLVM_BUILD_DIR}/bin/llvm-config" \
+    "${ABS_COMPILER_RT_DIR}"
+
+ninja
+
+# Copy selected output to the main tree.
+# Darwin doesn't support cp --parents, so pipe through tar instead.
+CLANG_VERSION=$("${ABS_LLVM_BUILD_DIR}/bin/clang" --version | \
+     sed -ne 's/clang version \([0-9]\.[0-9]\.[0-9]\).*/\1/p')
+ABS_LLVM_CLANG_LIB_DIR="${ABS_LLVM_BUILD_DIR}/lib/clang/${CLANG_VERSION}"
+tar -c *blacklist.txt | tar -C ${ABS_LLVM_CLANG_LIB_DIR} -xv
+tar -c include/sanitizer | tar -C ${ABS_LLVM_CLANG_LIB_DIR} -xv
+if [[ "${OS}" = "Darwin" ]]; then
+  tar -c lib/darwin | tar -C ${ABS_LLVM_CLANG_LIB_DIR} -xv
+else
+  tar -c lib/linux | tar -C ${ABS_LLVM_CLANG_LIB_DIR} -xv
+fi
+
+popd
+
+if [[ -n "${with_android}" ]]; then
+  # Make a standalone Android toolchain.
+  ${ANDROID_NDK_DIR}/build/tools/make-standalone-toolchain.sh \
+      --platform=android-19 \
+      --install-dir="${LLVM_BUILD_DIR}/android-toolchain" \
+      --system=linux-x86_64 \
+      --stl=stlport \
+      --toolchain=arm-linux-androideabi-4.9
+
+  # Android NDK r9d copies a broken unwind.h into the toolchain, see
+  # http://crbug.com/357890
+  rm -v "${LLVM_BUILD_DIR}"/android-toolchain/include/c++/*/unwind.h
+
+  # Build ASan runtime for Android in a separate build tree.
+  mkdir -p ${LLVM_BUILD_DIR}/android
+  pushd ${LLVM_BUILD_DIR}/android
+  rm -fv CMakeCache.txt
+  MACOSX_DEPLOYMENT_TARGET=${deployment_target} cmake -GNinja \
+      -DCMAKE_BUILD_TYPE=Release \
+      -DLLVM_ENABLE_ASSERTIONS=ON \
+      -DLLVM_ENABLE_THREADS=OFF \
+      -DCMAKE_C_COMPILER=${PWD}/../bin/clang \
+      -DCMAKE_CXX_COMPILER=${PWD}/../bin/clang++ \
+      -DLLVM_CONFIG_PATH=${PWD}/../bin/llvm-config \
+      -DCMAKE_C_FLAGS="--target=arm-linux-androideabi --sysroot=${PWD}/../android-toolchain/sysroot -B${PWD}/../android-toolchain" \
+      -DCMAKE_CXX_FLAGS="--target=arm-linux-androideabi --sysroot=${PWD}/../android-toolchain/sysroot -B${PWD}/../android-toolchain" \
+      -DANDROID=1 \
+      "${ABS_COMPILER_RT_DIR}"
+  ninja libclang_rt.asan-arm-android.so
+
+  # And copy it into the main build tree.
+  cp "$(find -name libclang_rt.asan-arm-android.so)" "${ABS_LLVM_CLANG_LIB_DIR}/lib/linux/"
+  popd
+fi
+
+if [[ -n "$run_tests" || -n "${LLVM_FORCE_HEAD_REVISION:-''}" ]]; then
+  # Run Chrome tool tests.
+  ninja -C "${LLVM_BUILD_DIR}" cr-check-all
+fi
+if [[ -n "$run_tests" ]]; then
+  # Run the LLVM and Clang tests.
+  ninja -C "${LLVM_BUILD_DIR}" check-all
+fi
+
+# After everything is done, log success for this revision.
+echo "${PACKAGE_VERSION}" > "${STAMP_FILE}"
diff --git a/tools/gn.py b/tools/gn.py
index 59142ba5374..b30d7744a9f 100755
--- a/tools/gn.py
+++ b/tools/gn.py
@@ -165,8 +165,10 @@ def to_gn_args(args, mode, arch, target_os):
   # TODO(zra): Investigate using clang with these configurations.
   # Clang compiles tcmalloc's inline assembly for ia32 on Linux wrong, so we
   # don't use clang in that configuration. Thus, we use gcc for ia32 *unless*
-  # a clang-based sanitizer is specified.
+  # asan or tsan is specified.
   has_clang = (host_os != 'win'
+               and args.os not in ['android']
+               and not gn_args['target_cpu'].startswith('arm')
                and not gn_args['target_cpu'].startswith('mips')
                and not ((gn_args['target_os'] == 'linux')
                         and (gn_args['host_cpu'] == 'x86')
@@ -246,7 +248,7 @@ def process_options(args):
       if os_name != 'android':
         print "Unsupported target os %s" % os_name
         return False
-      if not HOST_OS in ['linux', 'macos']:
+      if not HOST_OS in ['linux']:
         print ("Cross-compilation to %s is not supported on host os %s."
                % (os_name, HOST_OS))
         return False
@@ -365,8 +367,7 @@ def parse_args(args):
       type=int,
       help='Number of simultaneous GN invocations',
       dest='workers',
-      # Set to multiprocessing.cpu_count() when GN can be run in parallel.
-      default=1)
+      default=multiprocessing.cpu_count())
 
   options = parser.parse_args(args)
   if not process_options(options):
diff --git a/tools/ninja.py b/tools/ninja.py
index 7a2db651a7f..55d8d2ad8e4 100755
--- a/tools/ninja.py
+++ b/tools/ninja.py
@@ -90,7 +90,7 @@ def ProcessOptions(options, args):
       if os_name != 'android':
         print "Unsupported target os %s" % os_name
         return False
-      if not HOST_OS in ['linux', 'macos']:
+      if not HOST_OS in ['linux']:
         print ("Cross-compilation to %s is not supported on host os %s."
                % (os_name, HOST_OS))
         return False