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

chrome/browser/chromeos/background/desktop_background_observer.h

Index: chrome/browser/chromeos/background/desktop_background_observer.h
diff --git a/chrome/browser/chromeos/background/desktop_background_observer.h b/chrome/browser/chromeos/background/desktop_background_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..2fcca77203b3fc6774aa7dfff4678c703e1a94a1
--- /dev/null
+++ b/chrome/browser/chromeos/background/desktop_background_observer.h
@@ -0,0 +1,36 @@
+// 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_BACKGROUND_DESKTOP_BACKGROUND_OBSERVER_H_
+#define CHROME_BROWSER_CHROMEOS_BACKGROUND_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.
+class DesktopBackgroundObserver : public content::NotificationObserver{
+ public:
+  DesktopBackgroundObserver();
+  virtual ~DesktopBackgroundObserver();
+
+ private:
+  // Returns the index of user selected wallpaper from a default wallpaper list.
+  int GetUserWallpaperIndex();
+
+  // content::NotificationObserver implementation.
+  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_BACKGROUND_DESKTOP_BACKGROUND_OBSERVER_H_