Invalidate all wallpaper cache if display configuration changed

ash/default_user_wallpaper_delegate.h

 // Copyright 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.
 
 #ifndef ASH_DEFAULT_USER_WALLPAPER_DELEGATE_H_
 #define ASH_DEFAULT_USER_WALLPAPER_DELEGATE_H_
 
 #include "ash/ash_export.h"
 #include "ash/desktop_background/user_wallpaper_delegate.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 
 namespace ash {
 
 class ASH_EXPORT DefaultUserWallpaperDelegate : public UserWallpaperDelegate {
  public:
   DefaultUserWallpaperDelegate() {}
   virtual ~DefaultUserWallpaperDelegate() {}
 
   // UserWallpaperDelegate overrides:
   virtual int GetAnimationType() OVERRIDE;
   virtual int GetAnimationDurationOverride() OVERRIDE;
   virtual void SetAnimationDurationOverride(
       int animation_duration_in_ms) OVERRIDE;
   virtual bool ShouldShowInitialAnimation() OVERRIDE;
-  virtual void UpdateWallpaper() OVERRIDE;
+  virtual void UpdateWallpaper(bool clear_cache) OVERRIDE;
   virtual void InitializeWallpaper() OVERRIDE;
   virtual void OpenSetWallpaperPage() OVERRIDE;
   virtual bool CanOpenSetWallpaperPage() OVERRIDE;
   virtual void OnWallpaperAnimationFinished() OVERRIDE;
   virtual void OnWallpaperBootAnimationFinished() OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DefaultUserWallpaperDelegate);
 };
 
 }  // namespace ash
 
 #endif  // ASH_DEFAULT_USER_WALLPAPER_DELEGATE_H_