Implement all system menu title row buttons for Ash MD

ash/common/system/tiles/tray_tiles.h

 // Copyright 2016 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_COMMON_SYSTEM_TILES_TRAY_TILES_H_
 #define ASH_COMMON_SYSTEM_TILES_TRAY_TILES_H_
 
 #include "ash/ash_export.h"
 #include "ash/common/system/tray/system_tray_item.h"
 #include "base/macros.h"
 
 namespace ash {
 class SystemTray;
 class TilesDefaultView;
 
 // The tray item for the 'tiles' at the bottom of the system menu. Each tile is
 // an image button which does not reqire explanatory text, and thus does not
 // require its own dedicated row in the system menu.
 class ASH_EXPORT TrayTiles : public SystemTrayItem {
  public:
   explicit TrayTiles(SystemTray* system_tray);
   ~TrayTiles() override;
 
   // SystemTrayItem:
   views::View* CreateDefaultView(LoginStatus status) override;
   void DestroyDefaultView() override;
 
  private:
+  friend class TrayTilesTest;
+
   TilesDefaultView* default_view_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayTiles);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_TILES_TRAY_TILES_H_