Cleanup TrayCast with media-router only support in mind.

ash/common/system/chromeos/cast/tray_cast.h

Index: ash/common/system/chromeos/cast/tray_cast.h
diff --git a/ash/common/system/chromeos/cast/tray_cast.h b/ash/common/system/chromeos/cast/tray_cast.h
index afdb1c86c9efbf802c6681da717ee4bd23722149..dd20176072a09d9c358a43d40772f88ff8d1642c 100644
--- a/ash/common/system/chromeos/cast/tray_cast.h
+++ b/ash/common/system/chromeos/cast/tray_cast.h
@@ -58,10 +58,17 @@ class ASH_EXPORT TrayCast : public SystemTrayItem,
   // casting session.
   void UpdatePrimaryView();
 
+  // Returns true if there is an active cast route. The route may be DIAL based,
+  // such as casting YouTube where the cast sink directly streams content from
+  // another server. In that case, is_mirror_casting_ will be false since this
+  // device is not actively transmitting information to the cast sink.
+  bool HasActiveRoute();
+
   CastConfigDelegate::SinksAndRoutes sinks_and_routes_;
-  bool is_casting_ = false;
 
-  bool added_observer_ = false;
+  // True if there is a mirror-based cast session and the active-cast tray icon
+  // should be shown.
+  bool is_mirror_casting_ = false;
 
   // Not owned.
   tray::CastTrayView* tray_ = nullptr;