js_runtime: Split _asyncHelper into separate functions

pkg/compiler/lib/src/common_elements.dart

Index: pkg/compiler/lib/src/common_elements.dart
diff --git a/pkg/compiler/lib/src/common_elements.dart b/pkg/compiler/lib/src/common_elements.dart
index e113ed2d908b37c0f38595b9b7f5d2a3076358cd..f757dcc88f4154efc7c11eeaddfed3376880528c 100644
--- a/pkg/compiler/lib/src/common_elements.dart
+++ b/pkg/compiler/lib/src/common_elements.dart
@@ -501,7 +501,14 @@ class CommonElements {
   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");