Add @Native(...) annotation for native class names.

tests/compiler/dart2js_native/subclassing_5_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.
 
 import "package:expect/expect.dart";
-import 'dart:_js_helper' show Creates, setNativeSubclassDispatchRecord;
+import 'dart:_js_helper' show Native, Creates, setNativeSubclassDispatchRecord;
 import 'dart:_interceptors' show Interceptor, findInterceptorForType;
 
 // Test type checks.
 
 class I {}
 
 class M implements I {
   miz() => 'M';
 }
 
-class N native "N" {}
+@Native("N")
+class N {}
 
 class A extends N {}
 
 class B extends A with M {
 }
 
 class Checks<T> {
   bool isCheck(x) => x is T;
   void assignCheck(x) {
     T z = x;
@@ skipping 139 matching lines @@
     inscrutable(new Checks<M>().assignCheck)(b);
     inscrutable(new Checks<I>().assignCheck)(b);
 
     inscrutable(new Checks<B>().castCheck)(b);
     inscrutable(new Checks<A>().castCheck)(b);
     inscrutable(new Checks<N>().castCheck)(b);
     inscrutable(new Checks<M>().castCheck)(b);
     inscrutable(new Checks<I>().castCheck)(b);
   }
 }