Add UI for cast system tray integration

ash/system/chromeos/screen_security/screen_capture_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_SYSTEM_CHROMEOS_SCREEN_CAPTURE_SCREEN_CAPTURE_TRAY_ITEM_H_
 #define ASH_SYSTEM_CHROMEOS_SCREEN_CAPTURE_SCREEN_CAPTURE_TRAY_ITEM_H_
 
+#include "ash/shell_observer.h"
 #include "ash/system/chromeos/screen_security/screen_capture_observer.h"
 #include "ash/system/chromeos/screen_security/screen_tray_item.h"
 
 namespace views {
 class View;
 }
 
 namespace ash {
 
 class ASH_EXPORT ScreenCaptureTrayItem : public ScreenTrayItem,
-                                         public ScreenCaptureObserver {
+                                         public ScreenCaptureObserver,
+                                         public ShellObserver {
  public:
   explicit ScreenCaptureTrayItem(SystemTray* system_tray);
   ~ScreenCaptureTrayItem() override;
 
  private:
   // Overridden from SystemTrayItem.
   views::View* CreateTrayView(user::LoginStatus status) override;
   views::View* CreateDefaultView(user::LoginStatus status) override;
 
   // Overridden from ScreenTrayItem.
   void CreateOrUpdateNotification() override;
   std::string GetNotificationId() override;
 
   // Overridden from ScreenCaptureObserver.
   void OnScreenCaptureStart(
       const base::Closure& stop_callback,
       const base::string16& screen_capture_status) override;
   void OnScreenCaptureStop() override;
 
+  // Overridden from ShellObserver.
+  void OnCastingSessionStartedOrStopped(bool started) override;
+
   base::string16 screen_capture_status_;
+  bool is_casting_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenCaptureTrayItem);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_CHROMEOS_SCREEN_CAPTURE_SCREEN_CAPTURE_TRAY_ITEM_H_