make StackingClient dispatch to either ash or desktop

ash/shell/shell_delegate_impl.h

 // 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.
 
 #ifndef ASH_SHELL_SHELL_DELEGATE_IMPL_H_
 #define ASH_SHELL_SHELL_DELEGATE_IMPL_H_
 
 #include "ash/shell_delegate.h"
 #include "base/compiler_specific.h"
 
@@ skipping 41 matching lines @@
   virtual void OpenFeedbackPage() OVERRIDE;
   virtual void RecordUserMetricsAction(UserMetricsAction action) OVERRIDE;
   virtual void HandleMediaNextTrack() OVERRIDE;
   virtual void HandleMediaPlayPause() OVERRIDE;
   virtual void HandleMediaPrevTrack() OVERRIDE;
   virtual string16 GetTimeRemainingString(base::TimeDelta delta) OVERRIDE;
   virtual void SaveScreenMagnifierScale(double scale) OVERRIDE;
   virtual double GetSavedScreenMagnifierScale() OVERRIDE;
   virtual ui::MenuModel* CreateContextMenu(
       aura::RootWindow* root_window) OVERRIDE;
+  virtual aura::client::StackingClient* CreateStackingClient() OVERRIDE;
 
  private:
   // Used to update Launcher. Owned by main.
   WindowWatcher* watcher_;
 
   LauncherDelegateImpl* launcher_delegate_;
 
   bool locked_;
   bool spoken_feedback_enabled_;
 
   DISALLOW_COPY_AND_ASSIGN(ShellDelegateImpl);
 };
 
 }  // namespace shell
 }  // namespace ash
 
 #endif  // ASH_SHELL_SHELL_DELEGATE_IMPL_H_