ash: Display system background while loading wallpaper.

ash/desktop_background/desktop_background_controller.cc

Index: ash/desktop_background/desktop_background_controller.cc
diff --git a/ash/desktop_background/desktop_background_controller.cc b/ash/desktop_background/desktop_background_controller.cc
index 6f4d11b4b3ee7a4c91d70a8fce14d0721aa08687..4d084df5dbd47cec917fdbda768d0026c9d9d7b5 100644
--- a/ash/desktop_background/desktop_background_controller.cc
+++ b/ash/desktop_background/desktop_background_controller.cc
@@ -6,6 +6,7 @@
 
 #include "ash/desktop_background/desktop_background_view.h"
 #include "ash/desktop_background/desktop_background_widget_controller.h"
+#include "ash/root_window_controller.h"
 #include "ash/shell.h"
 #include "ash/shell_factory.h"
 #include "ash/shell_window_ids.h"
@@ -277,6 +278,7 @@ void DesktopBackgroundController::OnWallpaperLoadCompleted(
 
 void DesktopBackgroundController::NotifyAnimationFinished() {
   Shell* shell = Shell::GetInstance();
+  shell->GetPrimaryRootWindowController()->HandleDesktopBackgroundVisible();
   shell->user_wallpaper_delegate()->OnWallpaperAnimationFinished();
 }