Implementation of async-await transformation on js ast.

tests/language/await_for_test.dart

 // 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.
 
 import "dart:async";
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 
 class Trace {
   String trace = "";
@@ skipping 20 matching lines @@
   }
   t1.record("X");
 }
 
 Trace t2 = new Trace();
 
 consumeTwo() async {
   await for (var x in makeMeAStream()) {
     t2.record(x);
   }
-  t2.record("X");
+  t2.record("Y");
+}
+
+Trace t3 = new Trace();
+
+consumeNested() async {
+  await for (var x in makeMeAStream()) {
+    t3.record(x);
+    await for (var y in makeMeAStream()) {
+      t3.record(y);
+    }
+    t3.record("|");
+  }
+  t3.record("Z");
+}
+
+Trace t4 = new Trace();
+
+consumeSomeOfInfinite() async {
+  int i = 0;
+  await for (var x in infiniteStream()) {
+    i++;
+    if (i > 10) break;
+    t4.record(x);
+  }
+  t4.record("U");
 }
 
 main() {
   var f1 = consumeOne();
   t1.record("T1:");
 
   var f2 = consumeTwo();
   t2.record("T2:");
+ 
+  var f3 = consumeNested();
+  t3.record("T3:");
+ 
+  var f4 = consumeSomeOfInfinite();
+  t4.record("T4:");
 
   asyncStart();
-  Future.wait([f1, f2]).then((_) {
-    print("Trace 1: $t1");
-    print("Trace 2: $t2");
+  Future.wait([f1, f2, f3, f4]).then((_) {
     Expect.equals("T1:12345X", t1.toString());
-    Expect.equals("T2:12345X", t2.toString());
+    Expect.equals("T2:12345Y", t2.toString());
+    Expect.equals("T3:112345|212345|312345|412345|512345|Z", t3.toString());
+    Expect.equals("T4:12345678910U", t4.toString());
     asyncEnd();
   });
 }
 
-
 // Create a stream that produces numbers [1, 2, ... maxCount]
 Stream timedCounter(int maxCount) {
   StreamController controller;
   Timer timer;
   int counter = 0;
 
   void tick(_) {
     counter++;
     controller.add(counter); // Ask stream to send counter values as event.
     if (counter >= maxCount) {
@@ skipping 14 matching lines @@
   }
 
   controller = new StreamController(
       onListen: startTimer,
       onPause: stopTimer,
       onResume: startTimer,
       onCancel: stopTimer);
 
   return controller.stream;
 }
+
+// Create a stream that produces numbers [1, 2, ... ]
+Stream infiniteStream() {
+  StreamController controller;
+  Timer timer;
+  int counter = 0;
+
+  void tick(_) {
+    counter++;
+    controller.add(counter); // Ask stream to send counter values as event.
+  }
+
+  void startTimer() {
+    timer = new Timer.periodic(const Duration(milliseconds: 10), tick);
+  }
+
+  void stopTimer() {
+    if (timer != null) {
+      timer.cancel();
+      timer = null;
+    }
+  }
+
+  controller = new StreamController(
+      onListen: startTimer,
+      onPause: stopTimer,
+      onResume: startTimer,
+      onCancel: stopTimer);
+
+  return controller.stream;
+}