Merge request - fixes dart2js async problems.

sdk/lib/_internal/compiler/js_lib/shared/async_await_error_codes.dart

Index: sdk/lib/_internal/compiler/js_lib/shared/async_await_error_codes.dart
===================================================================
--- sdk/lib/_internal/compiler/js_lib/shared/async_await_error_codes.dart	(revision 0)
+++ sdk/lib/_internal/compiler/js_lib/shared/async_await_error_codes.dart	(working copy)
@@ -0,0 +1,10 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Contains error codes that transformed async/async* functions use to
+/// communicate with js_helper functions.
+
+const int SUCCESS = 0;
+const int ERROR = 1;
+const int STREAM_WAS_CANCELED = 2;