Move all wallpaper file loading and decoding from DesktopBackgroundController to WallpaperManager.

ash/desktop_background/wallpaper_resizer.h

Index: ash/desktop_background/wallpaper_resizer.h
diff --git a/ash/desktop_background/wallpaper_resizer.h b/ash/desktop_background/wallpaper_resizer.h
index fadfb445f0dca4a4f63ed0853807f3fc393c797e..a6a8d315f5920a903e2f32f76a376e14b830da72 100644
--- a/ash/desktop_background/wallpaper_resizer.h
+++ b/ash/desktop_background/wallpaper_resizer.h
@@ -40,6 +40,8 @@ class ASH_EXPORT WallpaperResizer {
   uint32_t original_image_id() const { return original_image_id_; }
   WallpaperLayout layout() const { return layout_; }
 
+  int resource_id() const { return resource_id_; }
+
   // Called on the UI thread to run Resize() on the worker pool and post an
   // OnResizeFinished() task back to the UI thread on completion.
   void StartResize();
@@ -63,6 +65,9 @@ class ASH_EXPORT WallpaperResizer {
   // Unique identifier corresponding to the original (i.e. pre-resize) |image_|.
   uint32_t original_image_id_;
 
+  // -1 if image was not obtained from resources.
+  const int resource_id_;
+
   gfx::Size target_size_;
 
   WallpaperLayout layout_;