gdk: master-clock: disable vsync throttling

When running with a master clock based on the GdkFrameClock, we get
synchronized with the compositor, so no need for throttling rendering.

In particular when dealing with foreign windows, we run into deadlocks
in Mesa because of the way the Mesa wayland backend is implemented [1].

[1] : http://cgit.freedesktop.org/mesa/mesa/tree/src/egl/drivers/dri2/platform_wayland.c#n330

https://bugzilla.gnome.org/show_bug.cgi?id=754671

clutter/gdk/clutter-master-clock-gdk.c

@@ -476,6 +476,9 @@ clutter_master_clock_gdk_init (ClutterMasterClockGdk *self)
   for (l = stages; l; l = l->next)
     clutter_master_clock_gdk_stage_added (manager, l->data, self);
 
+  /* Deactivate sync to vblank since we have clock to drive us from
+     the compositor. */
+  _clutter_set_sync_to_vblank (FALSE);
 
   if (G_UNLIKELY (clutter_paint_debug_flags & CLUTTER_DEBUG_CONTINUOUS_REDRAW))
     g_warning ("Continuous redraw is not supported with the GDK backend.");