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

tests/compiler/dart2js_native/super_property_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 "dart:_js_helper";
 import "package:expect/expect.dart";
 
 // Tests super setter where the HInvokeSuper is using interceptor aka
 // explicit-receiver calling convention.
 
-class A native "A" {
+@Native("A")
+class A {
   var foo;
   get_foo() => foo;
   set bar(value) => foo = value;
 }
 
-class B extends A native "B" {
+@Native("B")
+class B extends A {
   set foo(value) {
     super.foo = value;
   }
   get foo => super.foo;
 }
 
 class C {
   var foo;
   get_foo() => foo;
   set bar(value) => foo = value;
@@ skipping 29 matching lines @@
 
 main() {
   setup();
   var things = [makeA(), makeB(), new C(), new D()];
   var test = testThing;
   test(things[0]);
   test(things[1]);
   test(things[2]);
   test(things[3]);
 }