Reland: mash: Convert TrayBackgroundView to wm common types

ash/system/chromeos/virtual_keyboard/virtual_keyboard_tray.h

 // Copyright 2014 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_CHROMEOS_VIRTUAL_KEYBOARD_VIRTUAL_KEYBOARD_TRAY_H_
 #define ASH_SYSTEM_CHROMEOS_VIRTUAL_KEYBOARD_VIRTUAL_KEYBOARD_TRAY_H_
 
 #include "ash/common/keyboard/keyboard_ui_observer.h"
-#include "ash/system/tray/tray_background_view.h"
+#include "ash/common/system/tray/tray_background_view.h"
 #include "ash/system/user/login_status.h"
 #include "base/macros.h"
 #include "ui/views/controls/button/button.h"
 
 namespace views {
 class ImageButton;
 }
 
 namespace ash {
 class StatusAreaWidget;
@@ skipping 21 matching lines @@
 
  private:
   views::ImageButton* button_;  // Not owned.
 
   DISALLOW_COPY_AND_ASSIGN(VirtualKeyboardTray);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_CHROMEOS_VIRTUAL_KEYBOARD_VIRTUAL_KEYBOARD_TRAY_H_