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 2d860b7311a16478387d2315d1d28ee8424dbcaa..3f86e6cd5cf4a13a5848715632d1970f8663eb4f 100644
--- a/pkg/compiler/lib/src/common_elements.dart
+++ b/pkg/compiler/lib/src/common_elements.dart
@@ -507,7 +507,14 @@ 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");