Fix problems with async* and await for in dart2js.

sdk/lib/_internal/compiler/js_lib/js_helper.dart

 // Copyright (c) 2013, 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.
 
 library _js_helper;
 
 import 'dart:_async_await_error_codes' as async_error_codes;
 
 import 'dart:_js_embedded_names' show
     DEFERRED_LIBRARY_URIS,
@@ skipping 3734 matching lines @@
 /// A wrapper around a [StreamController] that remembers if that controller
 /// got a cancel.
 ///
 /// Also has a subSubscription that when not null will provide events for the
 /// stream, and will be paused and resumed along with this controller.
 class AsyncStarStreamController {
   StreamController controller;
   Stream get stream => controller.stream;
   bool stopRunning = false;
   bool isAdding = false;
-  bool get isPaused => controller.isPaused;
+  bool isPaused = false;
   add(event) => controller.add(event);
   addStream(Stream stream) {
     return controller.addStream(stream, cancelOnError: false);
   }
   addError(error, stackTrace) => controller.addError(error, stackTrace);
   close() => controller.close();
 
   AsyncStarStreamController(body) {
     controller = new StreamController(
       onListen: () {
         scheduleMicrotask(() {
           Function wrapped = _wrapJsFunctionForAsync(body,
                                                      async_error_codes.SUCCESS);
           wrapped(null);
         });
       },
-      onResume: () {
+      onPause: () {
+        isPaused = true;
+      }, onResume: () {
+        isPaused = false;
         if (!isAdding) {
           asyncStarHelper(null, body, this);
         }
       }, onCancel: () {
         stopRunning = true;
+        if (isPaused) asyncStarHelper(null, body, this);
       });
   }
 }
 
 makeAsyncStarController(body) {
   return new AsyncStarStreamController(body);
 }
 
 class IterationMarker {
   static const YIELD_SINGLE = 0;
@@ skipping 93 matching lines @@
   // This is a function that will return a helper function that does the
   // iteration of the sync*.
   //
   // Each invocation should give a body with fresh state.
   final dynamic /* js function */ _outerHelper;
 
   SyncStarIterable(this._outerHelper);
 
   Iterator get iterator => new SyncStarIterator(JS('', '#()', _outerHelper));
 }