Merge CommonElements and BackendHelpers!

tests/compiler/dart2js/resolution_test.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.
 
 // Test that resolution does not resolve things we know will not be
 // needed by the backend.
 
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'package:compiler/src/apiimpl.dart';
@@ skipping 84 matching lines @@
 void test(String code, void check(CompilerImpl compiler)) {
   Uri uri = new Uri(scheme: 'source');
   var compiler = compilerFor(code, uri);
   asyncTest(() => compiler.run(uri).then((_) {
         check(compiler);
       }));
 }
 
 void testHasRuntimeType(String code) {
   test(code, (compiler) {
-    var element = compiler.backend.helpers.createRuntimeType;
+    var element = compiler.commonElements.createRuntimeType;
     Expect.isTrue(
         compiler.enqueuer.resolution.processedEntities.contains(element));
   });
 }
 
 main() {
   test(NO_RUNTIME_TYPE, (compiler) {
-    var element = compiler.backend.helpers.createRuntimeType;
+    var element = compiler.commonElements.createRuntimeType;
     Expect.isFalse(
         compiler.enqueuer.resolution.processedEntities.contains(element));
   });
 
   testHasRuntimeType(HAS_RUNTIME_TYPE_1);
   testHasRuntimeType(HAS_RUNTIME_TYPE_2);
   testHasRuntimeType(HAS_RUNTIME_TYPE_3);
   testHasRuntimeType(HAS_RUNTIME_TYPE_4);
   testHasRuntimeType(HAS_RUNTIME_TYPE_5);
   testHasRuntimeType(HAS_RUNTIME_TYPE_6);
 }