Rename StackingClient -> WindowTreeClient

ui/aura/test/test_stacking_client.cc

-// Copyright (c) 2012 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/aura/test/test_stacking_client.h"
-
-#include "ui/aura/root_window.h"
-
-namespace aura {
-namespace test {
-
-TestStackingClient::TestStackingClient(RootWindow* root_window)
-    : root_window_(root_window) {
-  client::SetStackingClient(root_window_, this);
-}
-
-TestStackingClient::~TestStackingClient() {
-  client::SetStackingClient(root_window_, NULL);
-}
-
-Window* TestStackingClient::GetDefaultParent(Window* context,
-                                             Window* window,
-                                             const gfx::Rect& bounds) {
-  return root_window_;
-}
-
-}  // namespace test
-}  // namespace aura