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 dc6415d8cf99ba76418686f81a6087d35bfd61d7..a81abb330c2c9e525f0a33bb44e3409a02683380 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;
@@ -134,8 +136,14 @@ class ASH_EXPORT Shell {
   // Toggles app list.
   void ToggleAppList();
 
-  // Sets the desktop background mode.
-  void SetDesktopBackgroundMode(BackgroundMode mode);
+  // Sets the desktop background wallpaper.

[Ben Goodger (Google), 2012/03/09 23:20:17]

Can we pull all of this off onto a DesktopBackgroundController that the shell
owns, rather than just adding to the shell api

[bshe, 2012/03/12 00:14:25]

Done. I am not sure if you mean to pull the following two functions as well. It
makes sense to me to pull them to DesktopBackgroundController as well, since
they also control background. But I could be wrong. And I am happy to move them
back if I am wrong. Thanks! 

+  void SetDesktopBackgroundWallpaper(const SkBitmap& wallpaper);
+
+  // Sets the desktop background (image mode).
+  void SetDesktopBackgroundImageMode(const SkBitmap& wallpaper);
+
+  // Sets the desktop background (solid color mode).
+  void SetDesktopBackgroundSolidColorMode();
 
   // Returns true if the screen is locked.
   bool IsScreenLocked() const;
@@ -166,6 +174,9 @@ 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();
   }
@@ -256,6 +267,7 @@ 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_;