mash: Partially migrate ash/desktop_background to ash common types.

ash/shell_factory.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_SHELL_FACTORY_H_
-#define ASH_SHELL_FACTORY_H_
-
-#include "ash/ash_export.h"
-
-namespace aura {
-class RootWindow;
-}
-
-namespace gfx {
-class ImageSkia;
-}
-
-namespace views {
-class View;
-class Widget;
-}
-
-// Declarations of shell component factory functions.
-
-namespace ash {
-
-views::Widget* CreateDesktopBackground(aura::Window* root_window,
-                                       int container_id);
-
-ASH_EXPORT views::Widget* CreateStatusArea(views::View* contents);
-
-}  // namespace ash
-
-#endif  // ASH_SHELL_FACTORY_H_