Enable user change background image in settings page in Aura build.

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 4d70bbd0a61c944b9a61e1b7e2c360dc8322c4fb..1ab43c0cc5ebe7597818f0559b3966233e05178b 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -17,6 +17,7 @@
 #include "ui/gfx/size.h"
 
 class CommandLine;
+class SkBitmap;
 
 namespace aura {
 class EventFilter;
@@ -40,6 +41,7 @@ namespace ash {
 class AcceleratorController;
 class AudioController;
 class BrightnessController;
+class DesktopBackgroundController;
 class Launcher;
 class NestedDispatcherController;
 class PowerButtonController;
@@ -145,6 +147,9 @@ class ASH_EXPORT Shell {
   // Toggles app list.
   void ToggleAppList();
 
+  // Sets the desktop background wallpaper.
+  void SetDesktopBackgroundWallpaper(const SkBitmap& wallpaper);
+
   // Sets the desktop background mode.
   void SetDesktopBackgroundMode(BackgroundMode mode);
 
@@ -184,6 +189,9 @@ class ASH_EXPORT Shell {
   internal::PartialScreenshotEventFilter* partial_screenshot_filter() {
     return partial_screenshot_filter_.get();
   }
+  DesktopBackgroundController* desktop_background_controller() {
+    return desktop_background_controller_.get();
+  }
   PowerButtonController* power_button_controller() {
     return power_button_controller_.get();
   }
@@ -289,6 +297,7 @@ class ASH_EXPORT Shell {
   scoped_ptr<internal::ShadowController> shadow_controller_;
   scoped_ptr<internal::TooltipController> tooltip_controller_;
   scoped_ptr<internal::VisibilityController> visibility_controller_;
+  scoped_ptr<DesktopBackgroundController> desktop_background_controller_;
   scoped_ptr<PowerButtonController> power_button_controller_;
   scoped_ptr<VideoDetector> video_detector_;
   scoped_ptr<WindowCycleController> window_cycle_controller_;