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

tests/compiler/dart2js_native/native_class_fields_3_test.dart

 // Copyright (c) 2011, 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";
 
 // Verify that we can have fields with names that start with g and s even
 // though those names are reserved for getters and setters in minified mode.
 
 // Note: this works because end and send are both in the list of
 // reservedNativeProperties.  In general we don't check arbitrary
 // names for clashes because it's hard - subclasses can force superclasses
 // to rename getters, and that can force unrelated classes to change their
 // getters too if they have a property that has the same name.
-class A native "A" {
+@Native("A")
+class A {
   int bar;
   int g;
   int s;
   int end;
   int gend;
   int send;
   int gettersCalled;
   int settersCalled;
 }
 
@@ skipping 53 matching lines @@
   Expect.equals(42, foo.send);
   Expect.equals(271, foo.bar = 271);
   Expect.equals(271, foo.g = 271);
   Expect.equals(271, foo.s = 271);
   Expect.equals(271, foo.end = 271);
   Expect.equals(271, foo.gend = 271);
   Expect.equals(271, foo.send = 271);
   Expect.equals(6, foo.gettersCalled);
   Expect.equals(6, foo.settersCalled);
 }