Merge CommonElements and BackendHelpers!

pkg/compiler/lib/src/js_emitter/native_emitter.dart

Index: pkg/compiler/lib/src/js_emitter/native_emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/native_emitter.dart b/pkg/compiler/lib/src/js_emitter/native_emitter.dart
index ee23ef276aaa411632ac21a9bda2bcdca990c7f2..4dbceb87fdffeed23f9f835d72838b5ea68065ac 100644
--- a/pkg/compiler/lib/src/js_emitter/native_emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/native_emitter.dart
@@ -10,7 +10,6 @@ import '../elements/types.dart' show DartType, FunctionType;
 import '../elements/entities.dart';
 import '../js/js.dart' as jsAst;
 import '../js/js.dart' show js;
-import '../js_backend/backend_helpers.dart' show BackendHelpers;
 import '../js_backend/js_backend.dart' show JavaScriptBackend, Namer;
 import '../js_backend/interceptor_data.dart';
 import '../js_backend/native_data.dart';
@@ -42,8 +41,6 @@ class NativeEmitter {
 
   JavaScriptBackend get backend => compiler.backend;
 
-  BackendHelpers get helpers => backend.helpers;
-
   CodegenWorldBuilder get worldBuilder => compiler.codegenWorldBuilder;
 
   NativeData get nativeData => backend.nativeData;
@@ -104,7 +101,7 @@ class NativeEmitter {
         objectClass = cls;
         return;
       }
-      if (cls.element == helpers.jsInterceptorClass) {
+      if (cls.element == compiler.commonElements.jsInterceptorClass) {
         jsInterceptorClass = cls;
         return;
       }
@@ -271,7 +268,7 @@ class NativeEmitter {
 
   void potentiallyConvertDartClosuresToJs(List<jsAst.Statement> statements,
       FunctionEntity member, List<jsAst.Parameter> stubParameters) {
-    FunctionEntity converter = helpers.closureConverter;
+    FunctionEntity converter = compiler.commonElements.closureConverter;
     jsAst.Expression closureConverter =
         emitterTask.staticFunctionAccess(converter);
     worldBuilder.forEachParameter(member, (DartType type, String name) {