Fix error handling in dart2js async-await

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 1582 matching lines @@
   }
 
   Element getCreateInvocationMirror() {
     return findHelper(Compiler.CREATE_INVOCATION_MIRROR);
   }
 
   Element getCyclicThrowHelper() {
     return findHelper("throwCyclicInit");
   }
 
-  Element getThenHelper() {
-    return findHelper("thenHelper");
+  Element getAsyncHelper() {
+    return findHelper("asyncHelper");
   }
 
   Element getYieldStar() {
     ClassElement classElement = findHelper("IterationMarker");
     classElement.ensureResolved(compiler);
     return classElement.lookupLocalMember("yieldStar");
   }
 
   Element getYieldSingle() {
     ClassElement classElement = findHelper("IterationMarker");
     classElement.ensureResolved(compiler);
     return classElement.lookupLocalMember("yieldSingle");
   }
 
-  Element getStreamHelper() {
-    return findHelper("streamHelper");
+  Element getAsyncStarHelper() {
+    return findHelper("asyncStarHelper");
   }
 
   Element getStreamOfController() {
     return findHelper("streamOfController");
   }
 
   Element getEndOfIteration() {
     ClassElement classElement = findHelper("IterationMarker");
     classElement.ensureResolved(compiler);
     return classElement.lookupLocalMember("endOfIteration");
@@ skipping 767 matching lines @@
         : "out";
     String outName = outPath.substring(outPath.lastIndexOf('/') + 1);
     String extension = addExtension ? ".part.js" : "";
     return "${outName}_$name$extension";
   }
 
   void registerAsyncMarker(FunctionElement element,
                            Enqueuer enqueuer,
                            Registry registry) {
     if (element.asyncMarker == AsyncMarker.ASYNC) {
-      enqueue(enqueuer, getThenHelper(), registry);
+      enqueue(enqueuer, getAsyncHelper(), registry);
       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, getAsyncStarHelper(), 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.
@@ skipping 252 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);
 }