Preload default wallpaper.

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/desktop_background/desktop_background_resources.h"
 #include "ash/wm/window_animations.h"
@@ skipping 52 matching lines @@
 
   WallpaperLayout GetWallpaperLayout() const;
 
   // Provides current image on the background, or empty SkBitmap if there is
   // no image, e.g. background is solid color.
   SkBitmap GetCurrentWallpaperImage();
 
   // Initialize root window's background.
   void OnRootWindowAdded(aura::RootWindow* root_window);
 
+  // Loads default wallpaper at |index| asynchronously but does not set the
+  // loaded image to current wallpaper. Resource bundle will cache the loaded
+  // image.
+  void TriggerCacheDefaultWallpaper(int index);

[Nikita (slow), 2012/08/06 16:36:01]

nit: just CacheDefaultWallpaper ?

[bshe, 2012/08/07 15:18:57]

Done.

+
   // Loads default wallpaper at |index| asynchronously and sets to current
   // wallpaper after loaded.
   void SetDefaultWallpaper(int index);
 
   // Sets the user selected custom wallpaper. Called when user selected a file
   // from file system or changed the layout of wallpaper.
   void SetCustomWallpaper(const gfx::ImageSkia& wallpaper,
                           WallpaperLayout layout);
 
   // Cancels the current wallpaper loading operation.
@@ skipping 40 matching lines @@
   scoped_refptr<WallpaperOperation> wallpaper_op_;
 
   base::WeakPtrFactory<DesktopBackgroundController> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopBackgroundController);
 };
 
 }  // namespace ash
 
 #endif  // ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_