Bring in the latest Pub.

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//1293473003 .

CHANGELOG.md

@@ -52,8 +52,24 @@
 
 * Pub
 
+  * **Breaking:** various commands that previously ran `pub get` implicitly no
+    longer do so. Instead, they merely check to make sure the ".packages" file
+    is newer than the pubspec and the lock file, and fail if it's not.
+
+  * Added support for `--verbosity=error` and `--verbosity=warning`.
+
+  * `pub serve` now collapses multiple GET requests into a single line of
+    output. For full output, use `--verbose`.
+
+  * `pub deps` has improved formatting for circular dependencies on the
+    entrypoint package.
+
   * `pub run` and `pub global run`
 
+    * **Breaking:** to match the behavior of the Dart VM, executables no longer
+      run in checked mode by default. A `--checked` flag has been added to run
+      them in checked mode manually.
+
     * Faster start time for executables that don't import transformed code.
 
     * Binstubs for globally-activated executables are now written in the system

DEPS

@@ -84,7 +84,7 @@ vars = {
   "ply_rev": "@604b32590ffad5cbb82e4afef1d305512d06ae93",
   "plugin_tag": "@0.1.0",
   "pool_rev": "@e454b4b54d2987e8d2f0fbd3ac519641ada9bd0f",
-  "pub_rev": "@bc776a2e1364b5004d8e2601b2bafb8f93c6a396",
+  "pub_rev": "@4cc9aa3e6fd29c70b0929f3a827030b8a2ce0c7f",
   "pub_cache_tag": "@v0.1.0",
   "pub_semver_tag": "@1.2.1",
   "quiver_tag": "@0.21.4",