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

ash/system/cast/tray_cast.h

Index: ash/system/cast/tray_cast.h
diff --git a/ash/system/cast/tray_cast.h b/ash/system/cast/tray_cast.h
index 8474a754e2578cb8349dc549a723e56edf3c4d72..96bb903d84a913c118aae071c0c8be8518411721 100644
--- a/ash/system/cast/tray_cast.h
+++ b/ash/system/cast/tray_cast.h
@@ -48,7 +48,7 @@ class ASH_EXPORT TrayCast : public SystemTrayItem, public ShellObserver {
 
   // 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
@@ -58,14 +58,15 @@ class ASH_EXPORT TrayCast : public SystemTrayItem, public ShellObserver {
   // 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);