ash: Fix DesktopBackgroundController getting stuck.

ash/desktop_background/desktop_background_controller.h

Index: ash/desktop_background/desktop_background_controller.h
diff --git a/ash/desktop_background/desktop_background_controller.h b/ash/desktop_background/desktop_background_controller.h
index 4cfbc8ea5dfad68de57c45febbe3a28f060ca8d7..38c08c31c5b32af1abca439d693b2930670c399a 100644
--- a/ash/desktop_background/desktop_background_controller.h
+++ b/ash/desktop_background/desktop_background_controller.h
@@ -108,8 +108,8 @@ class ASH_EXPORT DesktopBackgroundController
   // from file system or changed the layout of wallpaper.
   void SetCustomWallpaper(const gfx::ImageSkia& image, WallpaperLayout layout);
 
-  // Cancels the current wallpaper loading operation.
-  void CancelPendingWallpaperOperation();
+  // Cancels |default_wallpaper_loader_| if non-NULL.
+  void CancelDefaultWallpaperLoader();
 
   // Creates an empty wallpaper. Some tests require a wallpaper widget is ready
   // when running. However, the wallpaper widgets are now created asynchronously
@@ -211,7 +211,8 @@ class ASH_EXPORT DesktopBackgroundController
 
   gfx::Size current_max_display_size_;
 
-  scoped_refptr<WallpaperLoader> wallpaper_loader_;
+  // Loads default wallpaper from disk.
+  scoped_refptr<WallpaperLoader> default_wallpaper_loader_;
 
   base::WeakPtrFactory<DesktopBackgroundController> weak_ptr_factory_;