Merge request - fixes dart2js async problems.

tests/language/async_return_types_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.
+
+import "dart:async";
+import "package:expect/expect.dart";
+import "package:async_helper/async_helper.dart";
+
+Future foo1() async {
+  return 3;
+}
+
+Future<int> foo2() async {
+  return 3;
+}
+
+Future<int> /// wrongTypeParameter: static type warning
+foo3() async {
+  return "String";
+}
+
+// Future<int, String> is treated like Future<dynamic>
+Future<int, String> /// tooManyTypeParameters: static type warning
+foo4() async {
+  return "String";
+}
+
+int /// wrongReturnType: static type warning, dynamic type error
+foo5() async {
+  return 3;
+}
+
+Future<int> foo6() async { 
+  // This is fine, the future is flattened
+  return new Future<int>.value(3);
+}
+
+Future<Future<int>> /// nestedFuture: static type warning
+foo7() async {
+  return new Future<int>.value(3);
+}
+
+test() async {
+  Expect.equals(3, await foo1());
+  Expect.equals(3, await foo2());
+  Expect.equals("String", await foo3());
+  Expect.equals("String", await foo4());
+  Expect.equals(3, await foo5());
+  Expect.equals(3, await await foo6());
+  Expect.equals(3, await await foo7());
+}
+
+main() {
+  asyncTest(test);
+}