Make the lifetime of wallpaper manager more clear.

chrome/browser/chromeos/chrome_browser_main_chromeos.cc

 // Copyright (c) 2013 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/chromeos/chrome_browser_main_chromeos.h"
 
 #include <string>
 #include <vector>
 
 #include "ash/ash_switches.h"
@@ skipping 709 matching lines @@
 
   media::SoundsManager::Shutdown();
 
   system::StatisticsProvider::GetInstance()->Shutdown();
 
   // Let the UserManager and WallpaperManager unregister itself as an observer
   // of the CrosSettings singleton before it is destroyed. This also ensures
   // that the UserManager has no URLRequest pending (see
   // http://crbug.com/276659).
   g_browser_process->platform_part()->user_manager()->Shutdown();
-  WallpaperManager::Get()->Shutdown();
+  WallpaperManager::Shutdown();
 
   // Let the DeviceDisablingManager unregister itself as an observer of the
   // CrosSettings singleton before it is destroyed.
   g_browser_process->platform_part()->ShutdownDeviceDisablingManager();
 
   // Let the AutomaticRebootManager unregister itself as an observer of several
   // subsystems.
   g_browser_process->platform_part()->ShutdownAutomaticRebootManager();
 
   // Clean up dependency on CrosSettings and stop pending data fetches.
@@ skipping 32 matching lines @@
   // Destroy DBus services immediately after threads are stopped.
   dbus_services_.reset();
 
   ChromeBrowserMainPartsLinux::PostDestroyThreads();
 
   // Destroy DeviceSettingsService after g_browser_process.
   DeviceSettingsService::Shutdown();
 }
 
 }  //  namespace chromeos