Merge CoreTypes and CoreClasses into CommonElements.

pkg/compiler/lib/src/common/backend_api.dart

 // Copyright (c) 2012, 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 dart2js.backend_api;
 
 import 'dart:async' show Future;
 
 import '../common.dart';
 import '../common/codegen.dart' show CodegenImpact;
@@ skipping 171 matching lines @@
   /// Returns whether or not `noSuchMethod` support has been enabled.
   bool get enabledNoSuchMethod => false;
 
   /// Called to enable support for isolates. Any backend specific [WorldImpact]
   /// of this is returned.
   WorldImpact enableIsolateSupport({bool forResolution});
 
   void registerConstSymbol(String name) {}
 
   ClassElement defaultSuperclass(ClassElement element) {
-    return compiler.coreClasses.objectClass;
+    return compiler.commonElements.objectClass;
   }
 
   bool isInterceptorClass(ClassElement element) => false;
 
   /// Returns `true` if [element] is implemented via typed JavaScript interop.
   // TODO(johnniwinther): Move this to [JavaScriptBackend].
   bool isJsInterop(Element element) => false;
 
   /// Returns `true` if the `native` pseudo keyword is supported for [library].
   bool canLibraryUseNative(LibraryElement library) {
@@ skipping 217 matching lines @@
   ClassElement get asyncStarStreamImplementation;
   ClassElement get indexableImplementation;
   ClassElement get mutableIndexableImplementation;
   ClassElement get indexingBehaviorImplementation;
   ClassElement get interceptorImplementation;
 
   bool isDefaultEqualityImplementation(Element element);
   bool isInterceptorClass(ClassElement cls);
   bool isNative(Element element);
 }