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

tests/compiler/dart2js_native/subclassing_2_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 findInterceptorForType;
 
 // Test calling convention of methods introduced on subclasses of native
 // classes.
 
 doFoo(r, x) => '$x,${r.oof()}';
 
-class A native "A" {
+@Native("A")
+class A {
   foo(x) => (doFoo)(this, x);
 }
 
 class B extends A {
   // [oof] is introduced only on this subclass of a native class.  It should
   // have interceptor calling convention.
   oof() => 'B';
 }
 
 B makeB() native;
@@ skipping 11 matching lines @@
 """;
 
 main() {
   setup();
 
   setNativeSubclassDispatchRecord(getBPrototype(), findInterceptorForType(B));
 
   B b = makeB();
   Expect.equals('1,B', b.foo(1));
 }