reland of https://codereview.chromium.org/11364053/ w/o removing the per-rootwindow stacking client

content/shell/shell_aura.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 "content/shell/shell.h"
 
 #include "base/command_line.h"
 #include "base/utf_string_conversions.h"
 #include "ui/aura/desktop/desktop_screen.h"
 #include "ui/aura/display_manager.h"
@@ skipping 275 matching lines @@
   aura::Env::GetInstance()->SetDisplayManager(new aura::SingleDisplayManager);
 #if defined(OS_CHROMEOS)
   stacking_client_ = new content::ShellStackingClientAsh();
   gfx::Screen::SetScreenInstance(
       gfx::SCREEN_TYPE_NATIVE, new ash::ScreenAsh);
 #else
   stacking_client_ = new aura::DesktopStackingClient();
   gfx::Screen::SetScreenInstance(
       gfx::SCREEN_TYPE_NATIVE, aura::CreateDesktopScreen());
 #endif
+  aura::client::SetStackingClient(stacking_client_);
   views_delegate_ = new ShellViewsDelegateAura();
 }
 
 void Shell::PlatformExit() {
   if (stacking_client_)
     delete stacking_client_;
   if (views_delegate_)
     delete views_delegate_;
 #if defined(OS_CHROMEOS)
   chromeos::DBusThreadManager::Shutdown();
@@ skipping 50 matching lines @@
 }
 
 void Shell::PlatformSetTitle(const string16& title) {
   ShellWindowDelegateView* delegate_view =
     static_cast<ShellWindowDelegateView*>(window_widget_->widget_delegate());
   delegate_view->SetWindowTitle(title);
   window_widget_->UpdateWindowTitle();
 }
 
 }  // namespace content