[mutter] Revert "monitor-manager-xrandr: Don't do extra work on RRScreenChangeNotify"

[Jasper St. Pierre <jstpierre src gnome org>]

commit 68542ae1effafc57e3f628bd70fd0c6994e3192d
Author: Rui Matos <tiagomatos gmail com>
Date:   Wed Dec 10 18:23:49 2014 +0100

    Revert "monitor-manager-xrandr: Don't do extra work on RRScreenChangeNotify"
    
    This reverts commit 47e339b46e80f01c2a4d020dbef7341e5a02b7eb. The
    approach that was used to reduce the amount of work we do on RR events
    to the necessary minimum is flawed. It assumes that, when the first
    event we see where the retrieved XRRScreenResources.timestamp is
    bigger than the previous, we already have all the data we need to
    rebuild our view of the world.
    
    That isn't true however, because the X server sends
    RRScreenChangeNotify events for every step of the configuration
    change, i.e. it lacks an atomic reconfiguration API. In particular, if
    the X screen size is one of the changes, when we rebuild our state and
    emit monitors-changed, the X screen size might still be the previous
    one and since we stop updating ourselves until another reconfiguration
    happens (noticed by looking at XRRScreenResources.timestamp) we end up
    with the wrong idea of the X screen size.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=738630

 src/backends/x11/meta-monitor-manager-xrandr.c |    8 ++------
 1 files changed, 2 insertions(+), 6 deletions(-)
---
diff --git a/src/backends/x11/meta-monitor-manager-xrandr.c b/src/backends/x11/meta-monitor-manager-xrandr.c
index 7a3926f..6abe6e0 100644
--- a/src/backends/x11/meta-monitor-manager-xrandr.c
+++ b/src/backends/x11/meta-monitor-manager-xrandr.c
@@ -1110,15 +1110,12 @@ meta_monitor_manager_xrandr_handle_xevent (MetaMonitorManagerXrandr *manager_xra
 {
   MetaMonitorManager *manager = META_MONITOR_MANAGER (manager_xrandr);
   gboolean hotplug;
-  Time old_timestamp;
 
   if ((event->type - manager_xrandr->rr_event_base) != RRScreenChangeNotify)
     return FALSE;
 
   XRRUpdateConfiguration (event);
 
-  old_timestamp = manager_xrandr->resources->timestamp;
-
   meta_monitor_manager_read_current_config (manager);
 
   hotplug = manager_xrandr->resources->timestamp < manager_xrandr->resources->configTimestamp;
@@ -1129,9 +1126,8 @@ meta_monitor_manager_xrandr_handle_xevent (MetaMonitorManagerXrandr *manager_xra
     }
   else
     {
-      /* If something else changed -- tell the world about it. */
-      if (old_timestamp < manager_xrandr->resources->timestamp)
-        meta_monitor_manager_rebuild_derived (manager);
+      /* Something else changed -- tell the world about it. */
+      meta_monitor_manager_rebuild_derived (manager);
     }
 
   return TRUE;