Fix UMR caused by ActiveWindowWatcher.

chrome/browser/gtk/browser_window_gtk.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 "chrome/browser/gtk/browser_window_gtk.h"
 
 #include <gdk/gdkkeysyms.h>
 #include <X11/XF86keysym.h>
 
 #include "app/resource_bundle.h"
@@ skipping 791 matching lines @@
       std::wstring* pref_name = Details<std::wstring>(details).ptr();
       if (*pref_name == prefs::kUseCustomChromeFrame) {
         UpdateCustomFrame();
       } else {
         NOTREACHED() << "Got pref change notification we didn't register for!";
       }
       break;
     }
 
     case NotificationType::ACTIVE_WINDOW_CHANGED: {
+      // Do nothing if we're in the process of closing the browser window.
+      if (!window_)
+        break;
+
       const GdkWindow* active_window = Details<const GdkWindow>(details).ptr();
       bool is_active = (GTK_WIDGET(window_)->window == active_window);
       bool changed = (is_active != is_active_);
       is_active_ = is_active;
       if (changed) {
         SetBackgroundColor();
         gdk_window_invalidate_rect(GTK_WIDGET(window_)->window,
                                    &GTK_WIDGET(window_)->allocation, TRUE);
         // For some reason, the above two calls cause the window shape to be
         // lost so reset it.
@@ skipping 622 matching lines @@
       *edge = GDK_WINDOW_EDGE_NORTH_EAST;
     } else if (y < bounds_.height() - kResizeAreaCornerSize) {
       *edge = GDK_WINDOW_EDGE_EAST;
     } else {
       *edge = GDK_WINDOW_EDGE_SOUTH_EAST;
     }
     return true;
   }
   NOTREACHED();
 }