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

tests/compiler/dart2js_native/native_class_inheritance4_frog_test.dart

 // Copyright (c) 2011, 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 "dart:_js_helper";
 import "package:expect/expect.dart";
 
 // Additional Dart code may be 'placed on' hidden native classes.  With
 // inheritance, the superclass method must not be reached by a call on the
 // subclass.
 
-class A native "A" {
+@Native("A")
+class A {
   var _field;
 
   int get X => _field;
   void set X(int x) { _field = x; }
 
   int method(int z) => _field + z;
 }
 
-class B extends A native "B" {
+@Native("B")
+class B extends A {
   var _field2;
 
   int get X => _field2;
   void set X(int x) { _field2 = x; }
 
   int method(int z) => _field2 + z;
 }
 
 A makeA() native { return new A(); }
 B makeB() native { return new B(); }
@@ skipping 107 matching lines @@
 }
 
 main() {
   testBasicA_dynamic();
   testBasicA_typed();
   testBasicB_dynamic();
   testBasicB_typed();
   testAB_dynamic();
   testAB_typed();
 }