[linux] Avoid crash when there's an X error during shutdown.

chrome/browser/ui/browser_list.cc

 // Copyright (c) 2010 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/browser_list.h"
 
 #include "base/logging.h"
 #include "base/message_loop.h"
 #include "base/metrics/histogram.h"
 #include "build/build_config.h"
@@ skipping 375 matching lines @@
   // Terminate will result in a CloseAllBrowsers() call, and once (and if)
   // that is done, will cause the application to exit cleanly.
   chrome_browser_application_mac::Terminate();
 #endif
 }
 
 // static
 void BrowserList::SessionEnding() {
   // EndSession is invoked once per frame. Only do something the first time.
   static bool already_ended = false;
-  if (already_ended)
+  // We may get called in the middle of shutdown, e.g. http://crbug.com/70852
+  // In this case, do nothing.
+  if (already_ended || !NotificationService::current())
     return;
   already_ended = true;
 
   browser_shutdown::OnShutdownStarting(browser_shutdown::END_SESSION);
 
   NotificationService::current()->Notify(
       NotificationType::APP_EXITING,
       NotificationService::AllSources(),
       NotificationService::NoDetails());
 
@@ skipping 205 matching lines @@
     }
 
     TabContents* next_tab =
         (*browser_iterator_)->GetTabContentsAt(web_view_index_);
     if (next_tab) {
       cur_ = next_tab;
       return;
     }
   }
 }