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

tests/compiler/dart2js_native/native_no_such_method_exception3_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:mirrors" show reflect;
+import "dart:_js_helper";
 import "package:expect/expect.dart";
 
 class GetName {
   foo(x, y, [z]) => "foo";
 }
 
 String getName(im) => reflect(new GetName()).delegate(im);
 
-class A native "A" {
+@Native("A")
+class A {
   bar() => 42;
 }
 
-class B native "B" {
+@Native("B")
+class B {
   foo() => 42;
 }
 
 class C {
   static create() => new C();
   noSuchMethod(x) => "${getName(x)}:${x.positionalArguments}";
 }
 
 makeA() native;
 
@@ skipping 10 matching lines @@
   try {
     a.foo();
   } on NoSuchMethodError catch (e) {
     exception = e;
   }
   Expect.isNotNull(exception);
   var c = C.create();
   Expect.equals("foo:[1, 2]", c.foo(1, 2));
   Expect.equals("foo:[3, 4, 5]", c.foo(3, 4, 5));
 }