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..b31a21464120ef1ecdff7e6f8e64f0ecb3c23329 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;
 
@@ -46,19 +47,51 @@ class ASH_EXPORT DesktopBackgroundController {
     return desktop_background_mode_;
   }
 
-  // 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.
-  void SetDesktopBackgroundImageMode();
+  // Load default wallpaper at |index| asynchronously and set to current
+  // wallpaper after loaded.
+  void SetDefaultWallpaper(int index);
+
+  // Cancel the current wallpaper loading operation.
+  void CancelPendingWallpaperOperation();
+
+  // Load logged in user wallpaper asynchronously and set to current wallpaper
+  // after loaded.
+  void SetLoggedInUserWallpaper();
 
   // Sets the desktop background to solid color mode and create a solid color
   // layout.
   void SetDesktopBackgroundSolidColorMode();
 
  private:
+  // An operation to asynchronously load wallpaper.
+  class WallpaperOperation;
+
+  // 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.
+  void SetDesktopBackgroundImageMode(scoped_refptr<WallpaperOperation> wo);
+
+  // Default wallpapper loaded, set the background mode to image mode.
+  void OnWallpaperLoadCompleted(scoped_refptr<WallpaperOperation> wo);
+
+  // Create an empty wallpaper. Some tests require a wallpaper widget is ready
+  // when running. However, the wallpaper widgets are now created asynchronously
+  // . If loading a real wallpaper, there are cases that these tests crash
+  // because the required widget is not ready. This function synchronously
+  // creates an empty widget for those tests to prevent crashes. An example test
+  // is SystemGestureEventFilterTest.ThreeFingerSwipe.
+  void CreateEmptyWallpaper();
+
   // Can change at runtime.
   BackgroundMode desktop_background_mode_;
 
+  // The previous successfully loaded wallpaper.
+  int previous_index_;
+
+  scoped_refptr<WallpaperOperation> wallpaper_op_;
+
+  base::WeakPtrFactory<DesktopBackgroundController> weak_ptr_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(DesktopBackgroundController);
 };