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

chrome/browser/ui/ash/chrome_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 "chrome/browser/ui/ash/chrome_shell_delegate.h"
 
 #include "ash/launcher/launcher_types.h"
 #include "ash/system/tray/system_tray_delegate.h"
+#include "ash/wm/stacking_controller.h"
 #include "ash/wm/window_util.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "chrome/browser/chromeos/login/screen_locker.h"
 #include "chrome/browser/extensions/api/terminal/terminal_extension_helper.h"
 #include "chrome/browser/lifetime/application_lifetime.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "chrome/browser/profiles/profile_manager.h"
 #include "chrome/browser/sessions/tab_restore_service.h"
 #include "chrome/browser/sessions/tab_restore_service_factory.h"
@@ skipping 445 matching lines @@
     return profile->GetPrefs()->GetDouble(prefs::kScreenMagnifierScale);
 #endif
   return std::numeric_limits<double>::min();
 }
 
 ui::MenuModel* ChromeShellDelegate::CreateContextMenu(aura::RootWindow* root) {
   DCHECK(launcher_delegate_);
   return new LauncherContextMenu(launcher_delegate_, root);
 }
 
+aura::client::StackingClient* ChromeShellDelegate::CreateStackingClient() {
+  return new ash::StackingController;
+}
+
 void ChromeShellDelegate::Observe(int type,
                                   const content::NotificationSource& source,
                                   const content::NotificationDetails& details) {
 #if defined(OS_CHROMEOS)
   switch (type) {
     case chrome::NOTIFICATION_LOGIN_USER_PROFILE_PREPARED:
       ash::Shell::GetInstance()->CreateLauncher();
       break;
     case chrome::NOTIFICATION_SESSION_STARTED:
       ash::Shell::GetInstance()->ShowLauncher();
       break;
     default:
       NOTREACHED() << "Unexpected notification " << type;
   }
 #else
   // MSVC++ warns about switch statements without any cases.
   NOTREACHED() << "Unexpected notification " << type;
 #endif
 }