[mutter] stage: Keep a pointer to the backend

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit f5958fa473c053cedaad2ca905caf28f09917660
Author: Jonas Ådahl <jadahl gmail com>
Date:   Wed Jul 29 10:11:08 2020 +0200

    stage: Keep a pointer to the backend
    
    Will be used later.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1391

 src/backends/meta-stage.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/src/backends/meta-stage.c b/src/backends/meta-stage.c
index 072241ec99..2cda7d471e 100644
--- a/src/backends/meta-stage.c
+++ b/src/backends/meta-stage.c
@@ -64,6 +64,8 @@ struct _MetaStage
 {
   ClutterStage parent;
 
+  MetaBackend *backend;
+
   GPtrArray *watchers[N_WATCH_MODES];
 
   GList *overlays;
@@ -305,6 +307,7 @@ meta_stage_new (MetaBackend *backend)
   MetaMonitorManager *monitor_manager;
 
   stage = g_object_new (META_TYPE_STAGE, NULL);
+  stage->backend = backend;
 
   monitor_manager = meta_backend_get_monitor_manager (backend);
   g_signal_connect (monitor_manager, "power-save-mode-changed",