make StackingClient dispatch to either ash or desktop

ui/aura/desktop/desktop_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/desktop/desktop_stacking_client.h"
 
 #include "ui/aura/client/activation_client.h"
 #include "ui/aura/client/default_capture_client.h"
 #include "ui/aura/desktop/desktop_activation_client.h"
 #include "ui/aura/focus_manager.h"
 #include "ui/aura/root_window.h"
 #include "ui/aura/shared/compound_event_filter.h"
 #include "ui/aura/shared/input_method_event_filter.h"
 #include "ui/aura/window.h"
 
 namespace aura {
 
 DesktopStackingClient::DesktopStackingClient()
     : window_event_filter_(NULL) {
-  client::SetStackingClient(this);
 }
 
 DesktopStackingClient::~DesktopStackingClient() {
   if (window_event_filter_)
     window_event_filter_->RemoveFilter(input_method_filter_.get());
 
   client::SetStackingClient(NULL);
 }
 
-Window* DesktopStackingClient::GetDefaultParent(Window* window,
+Window* DesktopStackingClient::GetDefaultParent(Window* context,
+                                                Window* window,
                                                 const gfx::Rect& bounds) {
   if (!null_parent_.get())
     CreateNULLParent();
 
   return null_parent_.get();
 }
 
 void DesktopStackingClient::CreateNULLParent() {
   focus_manager_.reset(new FocusManager);
 
@@ skipping 10 matching lines @@
   null_parent_->SetEventFilter(window_event_filter_);
 
   input_method_filter_.reset(new shared::InputMethodEventFilter);
   input_method_filter_->SetInputMethodPropertyInRootWindow(null_parent_.get());
   window_event_filter_->AddFilter(input_method_filter_.get());
 
   capture_client_.reset(new client::DefaultCaptureClient(null_parent_.get()));
 }
 
 }  // namespace aura