Asynchronously load wallpapers when user pod is selected.

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 b603fbde546a71f3d1ec5cc661419252259394d7..92536b6d887b20729f09de54b36480baae54408d 100644
--- a/ash/desktop_background/desktop_background_controller.h
+++ b/ash/desktop_background/desktop_background_controller.h
@@ -9,6 +9,7 @@
 #include "ash/ash_export.h"
 #include "ash/desktop_background/desktop_background_resources.h"
 #include "base/basictypes.h"
+#include "base/memory/weak_ptr.h"
 
 class SkBitmap;
 
@@ -46,6 +47,18 @@ class ASH_EXPORT DesktopBackgroundController {
     return desktop_background_mode_;
   }
 
+  // Load default wallpaper at |index| asynchronously and set to current
+  // wallpaper after loaded.
+  void SetDefaultWallpaper(int index);
+
+  // Load guest wallpaper asynchronously and set to current wallpaper after
+  // loaded.
+  void SetGuestWallpaper();
+
+  // Load logged in user wallpaper asynchronously and set to current wallpaper
+  // after loaded.
+  void SetLoggedInUserWallpaper();
+
   // Sets the desktop background to image mode and create a new background
   // widget with user selected wallpaper or default wallpaper. Delete the old
   // widget if any.
@@ -56,8 +69,18 @@ class ASH_EXPORT DesktopBackgroundController {
   void SetDesktopBackgroundSolidColorMode();
 
  private:
+  // Start to load default wallpaper asynchronously.
+  void OnWallpaperLoadStarted(int index);
+
+  // Default wallpapper loaded, set the background mode to image mode.
+  void OnWallpaperLoadCompleted();
+
   // Can change at runtime.
   BackgroundMode desktop_background_mode_;
+  const SkBitmap* wallpaper_;
+  ImageLayout layout_;
+  int previous_index_;
+  base::WeakPtrFactory<DesktopBackgroundController> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopBackgroundController);
 };