Make gstreamer player backend reserve/release video resource.

Use request/release of various video related controls as an indication for the decision.

Change-Id: I3a2a288c7c46ca62459896745bbdda26961bb181
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>
Reviewed-by: Jonas Rabbe <jonas.rabbe@nokia.com>

src/plugins/gstreamer/mediaplayer/qgstreamerplayerservice.h

@@ -86,6 +86,10 @@ private:
     QMediaControl *m_videoWindow;
     QMediaControl *m_videoWidget;
 #endif
+
+    void increaseVideoRef();
+    void decreaseVideoRef();
+    int m_videoReferenceCount;
 };
 
 QT_END_NAMESPACE