make StackingClient dispatch to either ash or desktop

ash/wm/stacking_controller.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 "ash/wm/stacking_controller.h"
 
 #include "ash/display/display_controller.h"
 #include "ash/shell.h"
 #include "ash/shell_delegate.h"
 #include "ash/shell_window_ids.h"
@@ skipping 38 matching lines @@
   return window->transient_parent() &&
       window->GetProperty(aura::client::kModalKey) == ui::MODAL_TYPE_WINDOW;
 }
 
 }  // namespace
 
 ////////////////////////////////////////////////////////////////////////////////
 // StackingController, public:
 
 StackingController::StackingController() {
-  aura::client::SetStackingClient(this);
 }
 
 StackingController::~StackingController() {
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // StackingController, aura::StackingClient implementation:
 
-aura::Window* StackingController::GetDefaultParent(aura::Window* window,
+aura::Window* StackingController::GetDefaultParent(aura::Window* context,
+                                                   aura::Window* window,
                                                    const gfx::Rect& bounds) {
   aura::RootWindow* target_root = NULL;
   if (window->transient_parent()) {
     // Transient window should use the same root as its transient parent.
     target_root = window->transient_parent()->GetRootWindow();
   } else {
     target_root = FindContainerRoot(bounds);
   }
 
   switch (window->type()) {
@@ skipping 69 matching lines @@
         root_window->GetChildById(
             internal::kShellWindowId_AlwaysOnTopContainer));
     // RootWindow owns the AlwaysOnTopController object.
     root_window->SetProperty(kAlwaysOnTopControllerKey, controller);
   }
   return controller;
 }
 
 }  // namespace internal
 }  // namespace ash