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

tests/compiler/dart2js_native/native_mixin_multiple3_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";
 
 // Test that native classes and plain classes can access methods defined only by
 // the same mixin.
 
 
 class D extends Object with M1, M2, M3 {
 }
 
 class E extends D {
   foo() => 'E.foo';
 }
 
 class M1 { }
 
 class M2 {
   foo() => 'M2.foo';
 }
 
 class M3 { }
 
-class A native "A" {
+@Native("A")
+class A {
   foo() => 'A.foo';
 }
 
-class B extends A with M1, M2, M3 native "B" {}
+@Native("B")
+class B extends A with M1, M2, M3 {}
 
-class C extends B native "C" {
+@Native("C")
+class C extends B {
   foo() => 'C.foo';
 }
 
 makeA() native;
 makeB() native;
 makeC() native;
 
 void setup() native """
 function A() {}
 function B() {}
@@ skipping 33 matching lines @@
   var e = x[4];
 
   var f = callFoo;
 
   Expect.equals('A.foo', f(a));
   Expect.equals('M2.foo', f(b));
   Expect.equals('C.foo', f(c));
   Expect.equals('M2.foo', f(d));
   Expect.equals('E.foo', f(e));
 }