Merge CommonElements and BackendHelpers!

pkg/compiler/lib/src/inferrer/closure_tracer.dart

 // Copyright (c) 2013, 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.
 
 library compiler.src.inferrer.closure_tracer;
 
 import '../common/names.dart' show Names;
 import '../elements/elements.dart';
-import '../js_backend/backend_helpers.dart';
+import '../js_backend/backend.dart' show JavaScriptBackend;
 import '../types/types.dart' show TypeMask;
 import '../universe/selector.dart' show Selector;
 import 'debug.dart' as debug;
 import 'inferrer_engine.dart';
 import 'node_tracer.dart';
 import 'type_graph_nodes.dart';
 
 class ClosureTracerVisitor extends TracerVisitor {
   final Iterable<FunctionElement> tracedElements;
   final List<CallSiteTypeInformation> _callsToAnalyze =
@@ skipping 51 matching lines @@
       bailout('Passed to a closure');
     }
   }
 
   @override
   visitStaticCallSiteTypeInformation(StaticCallSiteTypeInformation info) {
     super.visitStaticCallSiteTypeInformation(info);
     Element called = info.calledElement;
     if (compiler.backend.isForeign(called)) {
       String name = called.name;
-      if (name == BackendHelpers.JS || name == 'DART_CLOSURE_TO_JS') {
+      if (name == JavaScriptBackend.JS || name == 'DART_CLOSURE_TO_JS') {
         bailout('Used in JS ${info.call}');
       }
     }
     if (called.isGetter &&
         info.selector != null &&
         info.selector.isCall &&
         inferrer.types.getInferredTypeOf(called) == currentUser) {
       // This node can be a closure call as well. For example, `foo()`
       // where `foo` is a getter.
       _registerCallForLaterAnalysis(info);
@@ skipping 42 matching lines @@
   @override
   visitStaticCallSiteTypeInformation(StaticCallSiteTypeInformation info) {
     super.visitStaticCallSiteTypeInformation(info);
     if (info.calledElement == tracedElements.first &&
         info.selector != null &&
         info.selector.isGetter) {
       addNewEscapeInformation(info);
     }
   }
 }