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

tests/compiler/dart2js_native/rti_only_native_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.
 
 // Regression test for a bug that was caused by uninstantiated classes being
 // added to emitted classes by runtime-type system.
 // See my explanation in https://codereview.chromium.org/14018036/.
 //   -- ahe
 
-class A native "A" {
+import "dart:_js_helper";
+
+@Native("A")
+class A {
   // Just making sure the field name is unique.
   var rti_only_native_test_field;
 }
 
 typedef fisk();
 
 main() {
   void foo(A x) {}
   var map = { 'a': 0, 'b': main };
   try {
     map.values.forEach((x) => x.rti_only_native_test_field);
   } finally {
     print(main is fisk);
     return;
   }
 }