make StackingClient dispatch to either ash or desktop

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(this);
 }
 
 TestStackingClient::~TestStackingClient() {
   client::SetStackingClient(NULL);
 }
 
-Window* TestStackingClient::GetDefaultParent(Window* window,
+Window* TestStackingClient::GetDefaultParent(Window* context,
+                                             Window* window,
                                              const gfx::Rect& bounds) {
   return root_window_;
 }
 
 }  // namespace test
 }  // namespace aura