Fix app_shell shutdown crash due to BrowserContextKeyedServices

chrome/browser/extensions/extension_system_factory.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_EXTENSION_SYSTEM_FACTORY_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_SYSTEM_FACTORY_H_
 
 #include "base/memory/singleton.h"
 #include "chrome/browser/extensions/extension_system.h"
 #include "components/browser_context_keyed_service/browser_context_keyed_service_factory.h"
@@ skipping 26 matching lines @@
 };
 
 // BrowserContextKeyedServiceFactory for ExtensionSystem.
 class ExtensionSystemFactory : public BrowserContextKeyedServiceFactory {
  public:
   // BrowserContextKeyedServiceFactory implementation:
   static ExtensionSystem* GetForProfile(Profile* profile);
 
   static ExtensionSystemFactory* GetInstance();
 
-  // Provides a custom ExtensionSystem to use instead of building a new
-  // ExtensionSystemImpl. The BrowserContextKeyedService system takes ownership.
-  void SetCustomInstance(ExtensionSystem* extension_system);
-
  private:
   friend struct DefaultSingletonTraits<ExtensionSystemFactory>;
 
   ExtensionSystemFactory();
   virtual ~ExtensionSystemFactory();
 
   virtual BrowserContextKeyedService* BuildServiceInstanceFor(
       content::BrowserContext* profile) const OVERRIDE;
   virtual content::BrowserContext* GetBrowserContextToUse(
       content::BrowserContext* context) const OVERRIDE;
   virtual bool ServiceIsCreatedWithBrowserContext() const OVERRIDE;
-
-  ExtensionSystem* custom_instance_;  // Not owned.
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_SYSTEM_FACTORY_H_