shutdown_media_server: Finalize rework of synchronization

* When the user isn't requesting a custom notification, it will
be a BMediaRoster job to do it.
* Reintroduce BMediaRoster::SyncToServices, this time based on local
message passing rather than a global semaphore.
* SyncToServices is used in launch_media_server to make the process
more launch_daemon safe and faster in the average case.
* It was an error to add notifications in the media_server.
* Fixes #12717.

headers/os/media/MediaRoster.h

@@ -44,6 +44,10 @@ public:
 	// Check if the media services are running.
 	static	bool				IsRunning();
 
+	// Wait until the media_server is running or the specified timeout
+	// is reached.
+			status_t			SyncToServices(bigtime_t timeout);
+
 	// Getting common instances of system nodes:
 			status_t			GetVideoInput(media_node* _node);
 			status_t			GetAudioInput(media_node* _node);

headers/private/media/MediaRosterEx.h

@@ -95,7 +95,13 @@ public:
 		void				RegisterLocalNode(BMediaNode* node);
 		void				UnregisterLocalNode(BMediaNode* node);
 
+		void				EnableLaunchNotification(bool enable,
+								bool autoExit);
+
 private:
+		bool				fLaunchNotification;
+		bool				fAutoExit;
+
 	friend class BMediaRoster;
 };
 

headers/private/media/ServerInterface.h

@@ -40,7 +40,10 @@ enum {
 enum {
 	// local media services status notification service
 	MEDIA_ROSTER_REQUEST_NOTIFICATIONS = 2000,
-	MEDIA_ROSTER_CANCEL_NOTIFICATIONS
+	MEDIA_ROSTER_CANCEL_NOTIFICATIONS,
+
+	// used to sync with media services startup
+	MEDIA_ROSTER_REGISTER_SYNC
 };
 
 // Raw port based communication