Commit 5b8ba60c was added because of a memory leak when gtksink was
used as renderer. Nonetheless the patch didn't consider two facts:
1\ that the gtk_sink element was in floating state
2\ there is another code path where the gtk_sink element is already
sank
Thus the correct fix, is not to ref and unref gtk_sink, but sink it.
https://bugzilla.gnome.org/show_bug.cgi?id=781904
There's a GstPlayerVideoRenderer interface now, which defines how video
rendering happens in GstPlayer. Included is an implementation for the
GstVideoOverlay interface, and inside the GTK example application one for
gtksink/gtkglsink.
