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

ash/desktop_background/desktop_background_controller.h

Index: ash/desktop_background/desktop_background_controller.h
diff --git a/ash/desktop_background/desktop_background_controller.h b/ash/desktop_background/desktop_background_controller.h
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index 0000000000000000000000000000000000000000..dbb3cddb2450560345559201b950dac87f321838
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+++ b/ash/desktop_background/desktop_background_controller.h
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+// 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"
+#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_