Get rid of the huge delay in background resize during rotation

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 115 matching lines @@
   // Moves all desktop components from one container to other across all root
   // windows. Returns true if a desktop moved.
   bool ReparentBackgroundWidgets(int src_container, int dst_container);
 
   // Returns id for background container for unlocked and locked states.
   int GetBackgroundContainerId(bool locked);
 
   // Send notification that background animation finished.
   void NotifyAnimationFinished();
 
-  // Reload the wallpaper.
-  void UpdateWallpaper();
+  // Reload the wallpaper. |clear_cache| specifies whether to clear the
+  // wallpaper cahce or not.
+  void UpdateWallpaper(bool clear_cache);
 
   void set_wallpaper_reload_delay_for_test(bool value) {
     wallpaper_reload_delay_ = value;
   }
 
   // Can change at runtime.
   bool locked_;
 
   BackgroundMode desktop_background_mode_;
 
   SkColor background_color_;
 
   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_