Don't add keep-alives for apps after the app keep-alive service has shut down.

apps/app_keep_alive_service.h

 // Copyright 2013 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 APPS_APP_KEEP_ALIVE_SERVICE_H_
 #define APPS_APP_KEEP_ALIVE_SERVICE_H_
 
 #include "apps/app_lifetime_monitor.h"
 #include "components/browser_context_keyed_service/browser_context_keyed_service.h"
 
@@ skipping 11 matching lines @@
   virtual void OnAppStop(Profile* profile, const std::string& app_id) OVERRIDE;
   virtual void OnAppActivated(Profile* profile,
                               const std::string& app_id) OVERRIDE;
   virtual void OnAppDeactivated(Profile* profile,
                                 const std::string& app_id) OVERRIDE;
   virtual void OnChromeTerminating() OVERRIDE;
 
  private:
   content::BrowserContext* context_;
   std::set<std::string> running_apps_;
+  bool shut_down_;
 
   DISALLOW_COPY_AND_ASSIGN(AppKeepAliveService);
 };
 
 }  // namespace apps
 
 #endif  // APPS_APP_KEEP_ALIVE_SERVICE_H_