[mutter] wayland: Collect frame completion time once for all surfaces

[Carlos Garnacho <carlosg src gnome org>]

commit d6d01c85a61aaad7ff468f7896d34efe17077c1a
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sun Apr 30 20:49:26 2017 +0200

    wayland: Collect frame completion time once for all surfaces
    
    Dispatch all surface frames with the same monotonic time to avoid
    querying it too often.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=782344

 src/wayland/meta-wayland.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/src/wayland/meta-wayland.c b/src/wayland/meta-wayland.c
index 03cccdb..7bbd096 100644
--- a/src/wayland/meta-wayland.c
+++ b/src/wayland/meta-wayland.c
@@ -179,12 +179,14 @@ meta_wayland_compositor_update (MetaWaylandCompositor *compositor,
 void
 meta_wayland_compositor_paint_finished (MetaWaylandCompositor *compositor)
 {
+  gint64 current_time = g_get_monotonic_time ();
+
   while (!wl_list_empty (&compositor->frame_callbacks))
     {
       MetaWaylandFrameCallback *callback =
         wl_container_of (compositor->frame_callbacks.next, callback, link);
 
-      wl_callback_send_done (callback->resource, g_get_monotonic_time () / 1000);
+      wl_callback_send_done (callback->resource, current_time / 1000);
       wl_resource_destroy (callback->resource);
     }
 }