Support async/await in the dart2js frontend.

tests/compiler/dart2js/async_await_syntax_test.dart

Index: tests/compiler/dart2js/async_await_syntax_test.dart
diff --git a/tests/compiler/dart2js/async_await_syntax_test.dart b/tests/compiler/dart2js/async_await_syntax_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..e42bda00472d1026268c66af455e20ba5726ab8d
--- /dev/null
+++ b/tests/compiler/dart2js/async_await_syntax_test.dart
@@ -0,0 +1,16 @@
+// Copyright (c) 2014, 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 that dart2js produces the expected static type warnings and
+// compile-time errors for these tests.
+
+import 'frontend_checker.dart';
+
+const List<String> TESTS = const <String>[
+  'compiler/dart2js/async_await_syntax.dart',
+];
+
+void main(List<String> arguments) {
+  check(TESTS, arguments: arguments, options: ['--enable-async']);
+}