wayland: Use a stage paint callback instead of a signal handler on "paint"

This is much more appropriate...

src/compositor/compositor.c

@@ -637,6 +637,8 @@ after_stage_paint (ClutterStage *stage,
 
   for (l = info->windows; l; l = l->next)
     meta_window_actor_post_paint (l->data);
+
+  meta_wayland_compositor_paint_finished (meta_wayland_compositor_get_default ());
 }
 
 static void

src/wayland/meta-wayland-private.h

@@ -109,5 +109,6 @@ void                    meta_wayland_buffer_reference           (MetaWaylandBuff
 
 void                    meta_wayland_compositor_update          (MetaWaylandCompositor *compositor,
                                                                  const ClutterEvent    *event);
+void                    meta_wayland_compositor_paint_finished  (MetaWaylandCompositor *compositor);
 
 #endif /* META_WAYLAND_PRIVATE_H */

src/wayland/meta-wayland.c

@@ -500,11 +500,9 @@ const static struct wl_compositor_interface meta_wayland_compositor_interface =
   meta_wayland_compositor_create_region
 };
 
-static void
-paint_finished_cb (ClutterActor *self, void *user_data)
+void
+meta_wayland_compositor_paint_finished (MetaWaylandCompositor *compositor)
 {
-  MetaWaylandCompositor *compositor = user_data;
-
   while (!wl_list_empty (&compositor->frame_callbacks))
     {
       MetaWaylandFrameCallback *callback =
@@ -711,8 +709,6 @@ meta_wayland_init (void)
   compositor->outputs = meta_wayland_compositor_update_outputs (compositor, monitors);
 
   compositor->stage = meta_wayland_stage_new ();
-  g_signal_connect_after (compositor->stage, "paint",
-                          G_CALLBACK (paint_finished_cb), compositor);
   g_signal_connect (compositor->stage, "destroy",
                     G_CALLBACK (stage_destroy_cb), NULL);