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

chrome/browser/chromeos/options2/desktop_background_observer.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 CHROME_BROWSER_CHROMEOS_OPTIONS2_DESKTOP_BACKGROUND_OBSERVER_H_
+#define CHROME_BROWSER_CHROMEOS_OPTIONS2_DESKTOP_BACKGROUND_OBSERVER_H_
+#pragma once
+
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
+
+namespace chromeos {
+
+// Listens for background change events and passes them to
+// the Aura shell's DesktopBackgroundController class.

[flackr, 2012/03/05 16:16:03]

This class seems misplaced / unnecessary. Aura shell DesktopBackgroundController
could directly listen for background change events.

[bshe, 2012/03/06 01:33:27]

Done.

+class DesktopBackgroundObserver : public content::NotificationObserver{
+ public:
+  DesktopBackgroundObserver();
+  virtual ~DesktopBackgroundObserver();
+ private:
+  virtual void Observe(int type,
+                        const content::NotificationSource& source,
+                        const content::NotificationDetails& details) OVERRIDE;
+
+  content::NotificationRegistrar registrar_;
+
+  DISALLOW_COPY_AND_ASSIGN(DesktopBackgroundObserver);
+};
+
+}  // namespace chromeos
+#endif  // CHROME_BROWSER_CHROMEOS_OPTIONS2_DESKTOP_BACKGROUND_OBSERVER_H_