Don't try to load an event page to fire an event if the browser is shutting down.

chrome/browser/extensions/lazy_background_task_queue.h

 // Copyright (c) 2012 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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_LAZY_BACKGROUND_TASK_QUEUE_H_
 #define CHROME_BROWSER_EXTENSIONS_LAZY_BACKGROUND_TASK_QUEUE_H_
 
 #include <map>
 #include <string>
 
@@ skipping 24 matching lines @@
 
   // Returns true if the task should be added to the queue (that is, if the
   // extension has a lazy background page that isn't ready yet). If the
   // extension has a lazy background page that is being suspended this method
   // cancels that suspension.
   bool ShouldEnqueueTask(Profile* profile, const Extension* extension);
 
   // Adds a task to the queue for a given extension. If this is the first
   // task added for the extension, its lazy background page will be loaded.
   // The task will be called either when the page is loaded, or when the
-  // page fails to load for some reason (e.g. a crash). In the latter case,
-  // the ExtensionHost parameter is NULL.
+  // page fails to load for some reason (e.g. a crash or browser
+  // shutdown). In the latter case, the ExtensionHost parameter is NULL.
   void AddPendingTask(
       Profile* profile,
       const std::string& extension_id,
       const PendingTask& task);
 
  private:
   // A map between an extension_id,Profile pair and the queue of tasks pending
   // the load of its background page.
   typedef std::string ExtensionID;
   typedef std::pair<Profile*, ExtensionID> PendingTasksKey;
@@ skipping 14 matching lines @@
       const Extension* extension);
 
   Profile* profile_;
   content::NotificationRegistrar registrar_;
   PendingTasksMap pending_tasks_;
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_LAZY_BACKGROUND_TASK_QUEUE_H_