[mutter] group: Convert code to XCB to prevent errors

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

commit 352cac385074046b01c3d5ca31aa47592c42a83a
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Wed Aug 5 13:37:24 2015 -0700

    group: Convert code to XCB to prevent errors
    
    Windows can disappear at any time because X11 is really cool and good,
    so just use XCB so we won't crash if the window disappears.

 src/x11/group.c |   21 ++++++++++++++++-----
 1 files changed, 16 insertions(+), 5 deletions(-)
---
diff --git a/src/x11/group.c b/src/x11/group.c
index 9e5b576..123b9e1 100644
--- a/src/x11/group.c
+++ b/src/x11/group.c
@@ -31,6 +31,7 @@
 #include "group-props.h"
 #include "window-private.h"
 #include <meta/window.h>
+#include <X11/Xlib-xcb.h>
 
 static MetaGroup*
 meta_group_new (MetaDisplay *display,
@@ -50,10 +51,18 @@ meta_group_new (MetaDisplay *display,
   group->group_leader = group_leader;
   group->refcount = 1; /* owned by caller, hash table has only weak ref */
 
-  XWindowAttributes attrs;
-  XGetWindowAttributes (display->xdisplay, group_leader, &attrs);
-  XSelectInput (display->xdisplay, group_leader,
-                attrs.your_event_mask | PropertyChangeMask);
+  xcb_connection_t *xcb_conn = XGetXCBConnection (display->xdisplay);
+  xcb_generic_error_t *e;
+  g_autofree xcb_get_window_attributes_reply_t *attrs =
+    xcb_get_window_attributes_reply (xcb_conn,
+                                     xcb_get_window_attributes (xcb_conn, group_leader),
+                                     &e);
+  if (e)
+    return NULL;
+
+  const uint32_t events[] = { attrs->your_event_mask | XCB_EVENT_MASK_PROPERTY_CHANGE };
+  xcb_change_window_attributes (xcb_conn, group_leader,
+                                XCB_CW_EVENT_MASK, events);
 
   if (display->groups_by_leader == NULL)
     display->groups_by_leader = g_hash_table_new (meta_unsigned_long_hash,
@@ -173,12 +182,14 @@ meta_window_compute_group (MetaWindow* window)
       window->group = group;
     }
 
+  if (!window->group)
+    return;
+
   window->group->windows = g_slist_prepend (window->group->windows, window);
 
   meta_topic (META_DEBUG_GROUPS,
               "Adding %s to group with leader 0x%lx\n",
               window->desc, group->group_leader);
-
 }
 
 static void