MacViews: Change Widget context type to NativeWindow

ui/views/test/views_test_helper.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/test/views_test_helper.h"
 
 namespace views {
 
 ViewsTestHelper::ViewsTestHelper() {
 }
 
 ViewsTestHelper::~ViewsTestHelper() {
 }
 
 void ViewsTestHelper::SetUp() {
 }
 
 void ViewsTestHelper::TearDown() {
 }
 
-gfx::NativeView ViewsTestHelper::GetContext() {
+gfx::NativeWindow ViewsTestHelper::GetContext() {
   return NULL;
 }
 
 }  // namespace views