mash: Move most files in //ash/system/tray to //ash/common/system/tray

ash/system/tray/tray_empty.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_SYSTEM_TRAY_TRAY_EMPTY_H_
-#define ASH_SYSTEM_TRAY_TRAY_EMPTY_H_
-
-#include "ash/common/system/tray/system_tray_item.h"
-#include "base/macros.h"
-
-namespace ash {
-
-class TrayEmpty : public SystemTrayItem {
- public:
-  explicit TrayEmpty(SystemTray* system_tray);
-  ~TrayEmpty() override;
-
- private:
-  // Overridden from SystemTrayItem.
-  views::View* CreateTrayView(LoginStatus status) override;
-  views::View* CreateDefaultView(LoginStatus status) override;
-  views::View* CreateDetailedView(LoginStatus status) override;
-  void DestroyTrayView() override;
-  void DestroyDefaultView() override;
-  void DestroyDetailedView() override;
-  void UpdateAfterLoginStatusChange(LoginStatus status) override;
-
-  DISALLOW_COPY_AND_ASSIGN(TrayEmpty);
-};
-
-}  // namespace ash
-
-#endif  // ASH_SYSTEM_TRAY_TRAY_EMPTY_H_