Update chromeos system menu buttons for MD.

ash/common/system/tray/tray_popup_label_button.h

 // Copyright 2013 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_TRAY_TRAY_POPUP_LABEL_BUTTON_H_
 #define ASH_COMMON_SYSTEM_TRAY_TRAY_POPUP_LABEL_BUTTON_H_
 
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "ui/views/controls/button/label_button.h"
 
 namespace ash {
 
 // A label button with custom alignment, border and focus border.
+// TODO(estade): deprecated for MD. Use CreateTrayPopupButton instead.
+// See crbug.com/614453
 class TrayPopupLabelButton : public views::LabelButton {
  public:
   TrayPopupLabelButton(views::ButtonListener* listener,
                        const base::string16& text);
   ~TrayPopupLabelButton() override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(TrayPopupLabelButton);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_TRAY_TRAY_POPUP_LABEL_BUTTON_H_