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

tests/compiler/dart2js_native/native_no_such_method_exception2_frog_test.dart

 // Copyright (c) 2012, 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";
 
-class A native "A" {
+@Native("A")
+class A {
 }
 
-class B extends A native "B" {
+@Native("B")
+class B extends A {
   foo() native;
 }
 
 makeA() native;
 makeB() native;
 
 setup() native """
 function inherits(child, parent) {
   if (child.prototype.__proto__) {
     child.prototype.__proto__ = parent.prototype;
@@ skipping 19 matching lines @@
   try {
     a.foo();
   } on NoSuchMethodError catch (e) {
     exception = e;
   }
   Expect.isNotNull(exception);
 
   var b = makeB();
   Expect.equals(42, b.foo());
 }