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

tests/compiler/dart2js_native/subclassing_super_field_1_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:_foreign_helper' show JS;
-import 'dart:_js_helper' show Creates, setNativeSubclassDispatchRecord;
+import 'dart:_js_helper' show Native, Creates, setNativeSubclassDispatchRecord;
 import 'dart:_interceptors' show
     findInterceptorForType, findConstructorForNativeSubclassType;
 
 // Test for shadowed fields in classes that extend native classes.
 
-class N native "N" {
+@Native("N")
+class N {
   N.init();
 }
 
 class A extends N {
   var foo = 111;
   A.init() : super.init();
 }
 
 class B extends A  {
   var foo = 222;
@@ skipping 30 matching lines @@
   JS('', '#(#)', constructor, b);
 
   print(b);
 
   Expect.equals(222, inscrutable(b).Bfoo());
   Expect.equals(111, inscrutable(b).Afoo());
 
   Expect.equals(222, b.Bfoo());
   Expect.equals(111, b.Afoo());
 }