Bring in the latest pub.

R=rnystrom@google.com

Review URL: https://codereview.chromium.org/2201943002 .

CHANGELOG.md

@@ -1,3 +1,41 @@
+## 1.19.0
+
+### Tool Changes
+
+* Pub
+  * Added the ability for packages to declare a constraint on the [Flutter][]
+    SDK:
+
+        environment:
+          flutter: ^0.1.2
+          sdk: >=1.19.0 <2.0.0
+
+    A Flutter constraint will only be satisfiable when pub is running in the
+    context of the `flutter` executable, and when the Flutter SDK version
+    matches the constraint.
+
+  * Added `sdk` as a new package source that fetches packages from a hard-coded
+    SDK. Currently only the `flutter` SDK is supported:
+
+        dependencies:
+          flutter_driver:
+            sdk: flutter
+            version: ^0.0.1
+
+    A Flutter `sdk` dependency will only be satisfiable when pub is running in
+    the context of the `flutter` executable, and when the Flutter SDK contains a
+    package with the given name whose version matches the constraint.
+
+  * Fixed a bug where packages from a hosted HTTP URL were considered the same
+    as packages from an otherwise-identical HTTPS URL.
+
+  * Fixed timer formatting for timers that lasted longer than a minute.
+
+  * Eliminate some false negatives when determining whether global executables
+    are on the user's executable path.
+
+[Flutter]: https://flutter.io/
+
 ## 1.18.0
 
 ### Core library changes

DEPS

@@ -35,7 +35,7 @@ vars = {
   "buildtools_revision": "@565d04e8741429fb1b4f26d102f2c6c3b849edeb",
 
   # Revisions of /third_party/* dependencies.
-  "args_tag": "@0.13.4",
+  "args_tag": "@0.13.5",
   "async_tag": "@1.10.0",
   "barback-0.13.0_rev": "@34853",
   "barback-0.14.0_rev": "@36398",
@@ -88,7 +88,7 @@ vars = {
   "pool_tag": "@1.2.1",
   "protobuf_tag": "@0.5.1+1",
   "pub_cache_tag": "@v0.1.0",
-  "pub_rev": "@488ab539770512a234f0a01b74882dcbb3f1a4da",
+  "pub_rev": "@391b445dc6b28958794658b18caedb69d8cf8719",
   "pub_semver_tag": "@1.2.1",
   "quiver_tag": "@0.21.4",
   "resource_rev":"@a49101ba2deb29c728acba6fb86000a8f730f4b1",