[mutter] kms: Assert that callbacks are outside of the impl context

[Jonas Ådahl <jadahl src gnome org>]

commit 4abec2f8e7c1bde160b91524755d65d770fbf0f2
Author: Jonas Ådahl <jadahl gmail com>
Date:   Fri Nov 8 23:51:40 2019 +0100

    kms: Assert that callbacks are outside of the impl context
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/930

 src/backends/native/meta-kms.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/src/backends/native/meta-kms.c b/src/backends/native/meta-kms.c
index 6ee21e60e..10cfef196 100644
--- a/src/backends/native/meta-kms.c
+++ b/src/backends/native/meta-kms.c
@@ -276,6 +276,8 @@ flush_callbacks (MetaKms *kms)
   GList *l;
   int callback_count = 0;
 
+  meta_assert_not_in_kms_impl (kms);
+
   for (l = kms->pending_callbacks; l; l = l->next)
     {
       MetaKmsCallbackData *callback_data = l->data;