[mutter/gbsneto/annoying-stuttering] monitor-manager: Don't notify unchanged power save mode

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

commit 4a184d74d565f819b13172f09ea752e0fd72eb73
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Sat Jul 6 20:23:57 2019 -0300

    monitor-manager: Don't notify unchanged power save mode
    
    Since 4cae9b5b1132, and indirectly before that as well, the
    MetaMonitorManager::power-save-mode-changed is emitted even
    when the power save mode didn't actually change.
    
    On Wayland, this causes a mode set and therefore a stuttering.
    It became more proeminent with the transactional KMS code.
    
    Only emit 'power-save-mode-changed' when the power save mode
    actually changed.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/674

 src/backends/meta-monitor-manager.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/src/backends/meta-monitor-manager.c b/src/backends/meta-monitor-manager.c
index d2cbe2ec8..41036ca2a 100644
--- a/src/backends/meta-monitor-manager.c
+++ b/src/backends/meta-monitor-manager.c
@@ -345,6 +345,9 @@ meta_monitor_manager_power_save_mode_changed (MetaMonitorManager *manager,
   MetaMonitorManagerPrivate *priv =
     meta_monitor_manager_get_instance_private (manager);
 
+  if (priv->power_save_mode == mode)
+    return;
+
   priv->power_save_mode = mode;
   g_signal_emit (manager, signals[POWER_SAVE_MODE_CHANGED], 0);
 }