Make the ChromeOS chromecast system tray integration use a private API.

ash/system/cast/tray_cast.h

 // Copyright 2015 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_CAST_TRAY_CAST_H_
 #define ASH_SYSTEM_CAST_TRAY_CAST_H_
 
 #include "ash/cast_config_delegate.h"
 #include "ash/shell_observer.h"
 #include "ash/system/tray/system_tray_item.h"
@@ skipping 30 matching lines @@
   void UpdateAfterShelfAlignmentChange(ShelfAlignment alignment) override;
 
   // Overridden from ShellObserver.
   void OnCastingSessionStartedOrStopped(bool started) override;
 
   // Returns true if the cast extension was detected.
   bool HasCastExtension();
 
   // Callback used to enable/disable the begin casting view depending on
   // if we have any cast receivers.
-  void UpdateCachedReceiverState(
+  void OnReceiversUpdated(
       const CastConfigDelegate::ReceiversAndActivites& receivers_activities);
 
   // This makes sure that the current view displayed in the tray is the correct
   // one, depending on if we are currently casting. If we're casting, then a
   // view with a stop button is displayed; otherwise, a view that links to a
   // detail view is displayed instead that allows the user to easily begin a
   // casting session.
   void UpdatePrimaryView();
 
+  CastConfigDelegate::ReceiversAndActivites receivers_and_activities_;
+  CastConfigDelegate::DeviceUpdateSubscription device_update_subscription_;
+  bool is_casting_ = false;
+
   // Not owned.
   tray::CastTrayView* tray_ = nullptr;
   tray::CastDuplexView* default_ = nullptr;
   tray::CastDetailedView* detailed_ = nullptr;
-  CastConfigDelegate* cast_config_delegate_;
 
-  bool has_cast_receivers_ = false;
-  bool is_casting_ = false;
   base::WeakPtrFactory<TrayCast> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayCast);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_CAST_TRAY_CAST_H_