Preload default wallpaper.

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 ec9fcab402e7ad63e84990968cbc212a5aac0c6b..edcd803a2f28e923301e6f9e8ecced9e8feda304 100644
--- a/ash/desktop_background/desktop_background_controller.h
+++ b/ash/desktop_background/desktop_background_controller.h
@@ -76,6 +76,11 @@ class ASH_EXPORT DesktopBackgroundController : public aura::WindowObserver {
   // 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 CacheDefaultWallpaper(int index);
+
   // Loads default wallpaper at |index| asynchronously and sets to current
   // wallpaper after loaded. When |force_reload| is true, reload wallpaper
   // for all root windows even if |index| is the same as current wallpaper. It
@@ -145,6 +150,9 @@ class ASH_EXPORT DesktopBackgroundController : public aura::WindowObserver {
   // Returns id for background container for unlocked and locked states.
   int GetBackgroundContainerId(bool locked);
 
+  // Returns the appropriate wallpaper resolution for all root windows.
+  WallpaperResolution GetAppropriateResolution();
+
   // Can change at runtime.
   bool locked_;