Implementation of async-await transformation on js ast.

tests/language/await_not_started_immediately_test.dart

Index: tests/language/await_not_started_immediately_test.dart
diff --git a/tests/standalone/io/regress_21987_test.dart b/tests/language/await_not_started_immediately_test.dart
similarity index 54%
copy from tests/standalone/io/regress_21987_test.dart
copy to tests/language/await_not_started_immediately_test.dart
index 7cc6308f56e15f25b756be549c3a980f0e101c4c..035885e09c23480054e0dcf5c31ff63ca3a35963 100644
--- a/tests/standalone/io/regress_21987_test.dart
+++ b/tests/language/await_not_started_immediately_test.dart
@@ -2,19 +2,21 @@
 // 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:io';
+// Test that an async function does not start immediately.
 
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 
-void main() {
-  if (Platform.isLinux) {
-    asyncStart();
-    var selfExe = new Link('/proc/self/exe');
-    Expect.isTrue(selfExe.targetSync().length > 0);
-    selfExe.target().then((target) {
-      Expect.isTrue(target.length > 0);
-      asyncEnd();
-    });
-  }
+var x = 0;
+
+foo() async {
+  x++;
+  await 1;
+  x++;
 }
+
+void main() {
+  asyncStart();
+  foo().then((_) => Expect.equals(2, x)).whenComplete(asyncEnd);
+  Expect.equals(0, x);
+}