[mutter/gnome-3-34] backends: Plug MetaKmsPageFlipData leak

[Carlos Garnacho <carlosg src gnome org>]

commit cc00e55513c4e9a086dba2909380312bcb9f64a9
Author: Carlos Garnacho <carlosg gnome org>
Date:   Mon Oct 21 18:55:12 2019 +0200

    backends: Plug MetaKmsPageFlipData leak
    
    If the page flip is postponed, keep a ref to it, but still unref it
    on the page flip callback anyways. Fix suggested by Jonas Ådahl.
    
    (cherry-picked from 668be1f4bd309fedc846a0022180aef5a9e44869)
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/873

 src/backends/native/meta-kms-impl-simple.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/src/backends/native/meta-kms-impl-simple.c b/src/backends/native/meta-kms-impl-simple.c
index 19c4b2b33..571dccf12 100644
--- a/src/backends/native/meta-kms-impl-simple.c
+++ b/src/backends/native/meta-kms-impl-simple.c
@@ -772,12 +772,14 @@ meta_kms_impl_simple_handle_page_flip_callback (MetaKmsImpl         *impl,
     {
       impl_simple->postponed_page_flip_datas =
         g_list_append (impl_simple->postponed_page_flip_datas,
-                       page_flip_data);
+                       meta_kms_page_flip_data_ref (page_flip_data));
     }
   else
     {
       meta_kms_page_flip_data_flipped_in_impl (page_flip_data);
     }
+
+  meta_kms_page_flip_data_unref (page_flip_data);
 }
 
 static void