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

tests/compiler/dart2js_native/subclassing_3_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 calling convention of methods introduced on subclasses of native
 // class of mixin.
 
 doFoo(r, x) => '$x,${r.oof()},${r.miz()}';
 
 class M {
   miz() => 'M';
 }
 
-class N native "N" {
+@Native("N")
+class N {
   foo(x) => (doFoo)(this, x);
 }
 
 class A extends N {}
 
 class B extends A with M {
   // [oof] is introduced only on this subclass of a native class.  It should
   // have interceptor calling convention.
   oof() => 'B';
   // [miz] is introduced only on the mixin-application A+M.
@@ skipping 12 matching lines @@
 """;
 
 main() {
   setup();
 
   setNativeSubclassDispatchRecord(getBPrototype(), findInterceptorForType(B));
 
   B b = makeB();
   Expect.equals('1,B,M', b.foo(1));
 }