make StackingClient dispatch to either ash or desktop

ash/test/test_shell_delegate.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/test/test_shell_delegate.h"
 
 #include <algorithm>
 
 #include "ash/caps_lock_delegate_stub.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
 #include "ash/test/test_launcher_delegate.h"
+#include "ash/wm/stacking_controller.h"
 #include "ash/wm/window_util.h"
 #include "content/public/test/test_browser_context.h"
 #include "ui/aura/window.h"
 
 namespace ash {
 namespace test {
 
 TestShellDelegate::TestShellDelegate()
     : locked_(false),
       spoken_feedback_enabled_(false),
@@ skipping 129 matching lines @@
 }
 
 ui::MenuModel* TestShellDelegate::CreateContextMenu(aura::RootWindow* root) {
   return NULL;
 }
 
 double TestShellDelegate::GetSavedScreenMagnifierScale() {
   return std::numeric_limits<double>::min();
 }
 
+aura::client::StackingClient* TestShellDelegate::CreateStackingClient() {
+  return new StackingController;
+}
+
 }  // namespace test
 }  // namespace ash