Merge request - fixes dart2js async problems.

tests/language/sync_generator3_test.dart

 // 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.
 
 // Test program for sync* generator functions and yielding in try blocks.
 
 import "package:expect/expect.dart";
 
 f() sync* {
   try {
@@ skipping 16 matching lines @@
 g() sync* {
   try {
     yield "a";
     throw "pow!";
   } finally {
     yield "b";
   }
 }
 
 test2() {
-  var s;
-  try {
-    s = g().toString();
-  } catch (e) {
-    Expect.equals("pow!", e);
-    Expect.equals("(a, b)", s);
-    print(s);
-  }
+  Iterator i = g().iterator;
+  Expect.isTrue(i.moveNext());
+  Expect.equals("a", i.current);
+  Expect.isTrue(i.moveNext());
+  Expect.equals("b", i.current);
+  Expect.throws(() => i.moveNext(), (error) => error == "pow!");
 }
 
 main() {
   test1();  /// test1: ok
   test2();  /// test2: ok
 }