The execution of an async* should only be scheduled when the stream is

pkg/compiler/lib/src/js_backend/backend.dart

 // Copyright (c) 2012, 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.
 
 part of js_backend;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 const bool USE_CPS_IR = const bool.fromEnvironment("USE_CPS_IR");
 
@@ skipping 1602 matching lines @@
   Element getYieldSingle() {
     ClassElement classElement = findHelper("IterationMarker");
     classElement.ensureResolved(compiler);
     return classElement.lookupLocalMember("yieldSingle");
   }
 
   Element getStreamHelper() {
     return findHelper("streamHelper");
   }
 
+  Element getStreamOfController() {
+    return findHelper("streamOfController");
+  }
+
   Element getEndOfIteration() {
     ClassElement classElement = findHelper("IterationMarker");
     classElement.ensureResolved(compiler);
     return classElement.lookupLocalMember("endOfIteration");
   }
 
   Element getSyncStarIterable() {
     ClassElement classElement = findHelper("SyncStarIterable");
     classElement.ensureResolved(compiler);
     return classElement;
@@ skipping 772 matching lines @@
       enqueue(enqueuer, getCompleterConstructor(), registry);
       enqueue(enqueuer, getStreamIteratorConstructor(), registry);
     } else if (element.asyncMarker == AsyncMarker.SYNC_STAR) {
       enqueuer.registerInstantiatedClass(getSyncStarIterable(), registry);
       enqueue(enqueuer, getSyncStarIterableConstructor(), registry);
       enqueue(enqueuer, getEndOfIteration(), registry);
       enqueue(enqueuer, getYieldStar(), registry);
     } else if (element.asyncMarker == AsyncMarker.ASYNC_STAR) {
       enqueuer.registerInstantiatedClass(getASyncStarController(), registry);
       enqueue(enqueuer, getStreamHelper(), registry);
+      enqueue(enqueuer, getStreamOfController(), registry);
       enqueue(enqueuer, getYieldSingle(), registry);
       enqueue(enqueuer, getYieldStar(), registry);
       enqueue(enqueuer, getASyncStarControllerConstructor(), registry);
       enqueue(enqueuer, getStreamIteratorConstructor(), registry);
     }
   }
 }
 
 /// Handling of special annotations for tests.
 class Annotations {
@@ skipping 251 matching lines @@
   }
 }
 
 /// Records that [constant] is used by the element behind [registry].
 class Dependency {
   final ConstantValue constant;
   final Element annotatedElement;
 
   const Dependency(this.constant, this.annotatedElement);
 }