Fix app_shell shutdown crash due to BrowserContextKeyedServices

apps/shell/shell_extensions_browser_client.cc

 // 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.
 
 #include "apps/shell/shell_extensions_browser_client.h"
 
 #include "apps/shell/shell_app_sorting.h"
+#include "apps/shell/shell_extension_system.h"
 #include "base/prefs/pref_service.h"
 #include "base/prefs/pref_service_factory.h"
 #include "base/prefs/testing_pref_store.h"
 #include "chrome/browser/extensions/extension_prefs.h"
 #include "components/user_prefs/pref_registry_syncable.h"
 #include "components/user_prefs/user_prefs.h"
 #include "extensions/browser/app_sorting.h"
 
 using content::BrowserContext;
 
@@ skipping 93 matching lines @@
 }
 
 content::JavaScriptDialogManager*
 ShellExtensionsBrowserClient::GetJavaScriptDialogManager() {
   // TODO(jamescook): Create a JavaScriptDialogManager or reuse the one from
   // content_shell.
   NOTREACHED();
   return NULL;
 }
 
+std::vector<BrowserContextKeyedServiceFactory*>
+ShellExtensionsBrowserClient::GetExtensionSystemDependencies() {
+  // No dependencies.
+  return std::vector<BrowserContextKeyedServiceFactory*>();
+}
+
+extensions::ExtensionSystem*
+ShellExtensionsBrowserClient::CreateExtensionSystem(BrowserContext* context) {
+  return new extensions::ShellExtensionSystem(context);
+}
+
 }  // namespace apps