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

ash/desktop_background/desktop_background_controller.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_
+#define ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_
+#pragma once
+
+#include "ash/ash_export.h"
+#include "base/basictypes.h"
+#include "content/public/browser/notification_observer.h"

[Ben Goodger (Google), 2012/03/08 16:35:01]

Ash can't depend on content.

[bshe, 2012/03/08 19:55:48]

I moved the observer code to
chrome/browser/chromeos/background/desktop_background_observer.h and initialize
this observer in the PreProfileInit function in chrome_browser_main_chromeos.cc
file. Not sure this is the best place to put the observer though. Do you have
any suggestion? Thanks.

+#include "content/public/browser/notification_registrar.h"
+#include "third_party/skia/include/core/SkBitmap.h"
+
+namespace ash {
+
+// A class to listen for login and desktop background change events and set the
+// corresponding default wallpaper in Aura shell.
+class ASH_EXPORT DesktopBackgroundController :
+    public content::NotificationObserver {
+ public:
+  DesktopBackgroundController();
+  virtual ~DesktopBackgroundController();
+
+  // Change the desktop background image to |wallpaper|.
+  void OnDesktopBackgroundChange(const SkBitmap& wallpaper);
+
+  // Returns the preset default wallpaper.
+  const SkBitmap& GetPresetWallpaper();
+
+  // Returns the user selected wallpaper from a default wallpaper list.
+  const SkBitmap& GetUserWallpaper();
+ private:
+  virtual void Observe(int type,
+                       const content::NotificationSource& source,
+                       const content::NotificationDetails& details) OVERRIDE;
+
+  content::NotificationRegistrar registrar_;
+
+  DISALLOW_COPY_AND_ASSIGN(DesktopBackgroundController);
+};
+
+}  // namespace ash
+
+#endif  // ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_