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..6168caaae3c02a888d0ad3a7427cb4f075de687e
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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 "ui/aura/root_window_observer.h"
+#include "third_party/skia/include/core/SkBitmap.h"
+
+namespace ash {
+
+// This probably needs to put to another place. But I am not sure where is the
+// best place. It's basically util function which used both by ash and by
+// webui handler.
+extern const int kDefaultWallpaperResources[];
+extern const int kDefaultWallpaperResourcesThumb[];
+extern const int kDefaultWallpaperCount;
+
+const SkBitmap& GetDefaultWallpaper(int index);
+const SkBitmap& GetDefaultWallpaperThumbnail(int index);
+
+class ASH_EXPORT DesktopBackgroundController : public aura::RootWindowObserver {
+ public:
+  DesktopBackgroundController();
+  virtual ~DesktopBackgroundController();
+  void OnDesktopBackgroundChange(int index);
+ private:
+  DISALLOW_COPY_AND_ASSIGN(DesktopBackgroundController);
+};
+
+}  // namespace ash
+
+#endif  // ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_