Fixes bug in ActiveWindowWatcherX. It appears that in newer versions...

app/active_window_watcher_x.cc

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <X11/Xlib.h>
 #include <gdk/gdk.h>
 #include <gdk/gdkx.h>
 
 #include "app/active_window_watcher_x.h"
 
@@ skipping 12 matching lines @@
 ActiveWindowWatcherX::ActiveWindowWatcherX() {
   Init();
 }
 
 void ActiveWindowWatcherX::Init() {
   GdkAtom kNetActiveWindow = gdk_atom_intern("_NET_ACTIVE_WINDOW", FALSE);
   kNetActiveWindowAtom = gdk_x11_atom_to_xatom_for_display(
       gdk_screen_get_display(gdk_screen_get_default()), kNetActiveWindow);
 
   GdkWindow* root = gdk_get_default_root_window();
+
   // Set up X Event filter to listen for PropertyChange X events.  These events
   // tell us when the active window changes.
-  gdk_window_add_filter(root, &ActiveWindowWatcherX::OnWindowXEvent, this);
-  XSelectInput(
-      GDK_WINDOW_XDISPLAY(root), GDK_WINDOW_XID(root), PropertyChangeMask);
+  // Don't use XSelectInput directly here, as gdk internally seems to cache the
+  // mask and reapply XSelectInput after this, resetting any mask we set here.
+  gdk_window_set_events(root,
+                        static_cast<GdkEventMask>(gdk_window_get_events(root) |
+                                                  GDK_PROPERTY_CHANGE_MASK));
+  gdk_window_add_filter(NULL, &ActiveWindowWatcherX::OnWindowXEvent, this);
 }
 
 void ActiveWindowWatcherX::NotifyActiveWindowChanged() {
   // We don't use gdk_screen_get_active_window() because it caches
   // whether or not the window manager supports _NET_ACTIVE_WINDOW.
   // This causes problems at startup for chromiumos.
   Atom type = None;
   int format = 0;  // size in bits of each item in 'property'
   long unsigned int num_items = 0, remaining_bytes = 0;
   unsigned char* property = NULL;
@@ skipping 33 matching lines @@
       window_watcher);
   XEvent* xev = static_cast<XEvent*>(xevent);
 
   if (xev->xany.type == PropertyNotify &&
       xev->xproperty.atom == kNetActiveWindowAtom) {
     watcher->NotifyActiveWindowChanged();
   }
 
   return GDK_FILTER_CONTINUE;
 }