Replace more ObserverList with base::ObserverList.

ash/desktop_background/desktop_background_controller.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_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_
 #define ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_
 
 #include "ash/ash_export.h"
 #include "ash/display/display_controller.h"
 #include "ash/shell_observer.h"
@@ skipping 130 matching lines @@
     wallpaper_reload_delay_ = value;
   }
 
   // Can change at runtime.
   bool locked_;
 
   BackgroundMode desktop_background_mode_;
 
   SkColor background_color_;
 
-  ObserverList<DesktopBackgroundControllerObserver> observers_;
+  base::ObserverList<DesktopBackgroundControllerObserver> observers_;
 
   // The current wallpaper.
   scoped_ptr<wallpaper::WallpaperResizer> current_wallpaper_;
 
   gfx::Size current_max_display_size_;
 
   base::OneShotTimer<DesktopBackgroundController> timer_;
 
   int wallpaper_reload_delay_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopBackgroundController);
 };
 
 }  // namespace ash
 
 #endif  // ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_