Introduce mash/shell

mash/wm/background_layout.h

 // Copyright 2015 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 MASH_WM_BACKGROUND_LAYOUT_H_
 #define MASH_WM_BACKGROUND_LAYOUT_H_
 
 #include "base/macros.h"
 #include "mash/wm/layout_manager.h"
 
 namespace mash {
 namespace wm {
 
 // Lays out the desktop background within background containers.
 class BackgroundLayout : public LayoutManager {
  public:
   explicit BackgroundLayout(mus::Window* owner);
   ~BackgroundLayout() override;
 
  private:
   // Overridden from LayoutManager:
-  void WindowAdded(mus::Window* window) override;
   void LayoutWindow(mus::Window* window) override;
 
   DISALLOW_COPY_AND_ASSIGN(BackgroundLayout);
 };
 
 }  // namespace wm
 }  // namespace mash
 
 #endif  // MASH_WM_BACKGROUND_LAYOUT_H_