js_runtime: Split _asyncHelper into separate functions

pkg/compiler/lib/src/common_elements.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.
 
 // TODO(sigmund): rename and move to common/elements.dart
 library dart2js.type_system;
 
 import 'common/names.dart' show Identifiers, Uris;
 import 'js_backend/constant_system_javascript.dart';
 import 'elements/types.dart';
@@ skipping 483 matching lines @@
         classElement == jsNullClass;
   }
 
   // From dart:async
   ClassEntity _findAsyncHelperClass(String name) =>
       _findClass(asyncLibrary, name);
 
   FunctionEntity _findAsyncHelperFunction(String name) =>
       _findLibraryMember(asyncLibrary, name);
 
-  FunctionEntity get asyncHelper => _findAsyncHelperFunction("_asyncHelper");
+  FunctionEntity get asyncHelperStart =>
+      _findAsyncHelperFunction("_asyncStart");
+  FunctionEntity get asyncHelperAwait =>
+      _findAsyncHelperFunction("_asyncAwait");
+  FunctionEntity get asyncHelperReturn =>
+      _findAsyncHelperFunction("_asyncReturn");
+  FunctionEntity get asyncHelperRethrow =>
+      _findAsyncHelperFunction("_asyncRethrow");
 
   FunctionEntity get wrapBody =>
       _findAsyncHelperFunction("_wrapJsFunctionForAsync");
 
   FunctionEntity get yieldStar => _env.lookupClassMember(
       _findAsyncHelperClass("_IterationMarker"), "yieldStar");
 
   FunctionEntity get yieldSingle => _env.lookupClassMember(
       _findAsyncHelperClass("_IterationMarker"), "yieldSingle");
 
@@ skipping 723 matching lines @@
   DartType getUnaliasedType(DartType type);
 
   /// Returns the [CallStructure] corresponding to calling [entity] with all
   /// arguments, both required and optional.
   CallStructure getCallStructure(FunctionEntity entity);
 
   /// Returns `true` if [member] a the synthetic getter `loadLibrary` injected
   /// on deferred libraries.
   bool isDeferredLoadLibraryGetter(MemberEntity member);
 }