Update chromeos system menu buttons for MD.

ash/common/system/chromeos/screen_security/screen_tray_item.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_CHROMEOS_SCREEN_SECURITY_SCREEN_TRAY_ITEM_H_
 #define ASH_COMMON_SYSTEM_CHROMEOS_SCREEN_SECURITY_SCREEN_TRAY_ITEM_H_
 
 #include <string>
 
 #include "ash/common/system/tray/system_tray.h"
@@ skipping 28 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(ScreenTrayView);
 };
 
 class ScreenStatusView : public views::View, public views::ButtonListener {
  public:
   ScreenStatusView(ScreenTrayItem* screen_tray_item,
                    const base::string16& label_text,
                    const base::string16& stop_button_text);
   ~ScreenStatusView() override;
 
-  // Overridden from views::View.
-  void Layout() override;
-
   // Overridden from views::ButtonListener.
   void ButtonPressed(views::Button* sender, const ui::Event& event) override;
 
   void CreateItems();
-  void Update();
+  void UpdateFromScreenTrayItem();
+
+ protected:
+  views::ImageView* icon() { return icon_; }
+  views::Label* label() { return label_; }
 
  private:
+  // The controller for this view. May be null.
   ScreenTrayItem* screen_tray_item_;
   views::ImageView* icon_;
   views::Label* label_;
-  TrayPopupLabelButton* stop_button_;
+  views::View* stop_button_;
   base::string16 label_text_;
   base::string16 stop_button_text_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenStatusView);
 };
 
 class ScreenNotificationDelegate : public message_center::NotificationDelegate {
  public:
   explicit ScreenNotificationDelegate(ScreenTrayItem* screen_tray);
 
@@ skipping 56 matching lines @@
   tray::ScreenStatusView* default_view_;
   bool is_started_;
   base::Closure stop_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenTrayItem);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_CHROMEOS_SCREEN_SECURITY_SCREEN_TRAY_ITEM_H_