Fix app_shell shutdown crash due to BrowserContextKeyedServices

chrome/browser/extensions/extension_system_factory.h

Index: chrome/browser/extensions/extension_system_factory.h
diff --git a/chrome/browser/extensions/extension_system_factory.h b/chrome/browser/extensions/extension_system_factory.h
index 1f8a6530befdd5c3fb8aa53589701a51946c9407..280db7ae73b55750b03e42145f8a9adc0dba7f2e 100644
--- a/chrome/browser/extensions/extension_system_factory.h
+++ b/chrome/browser/extensions/extension_system_factory.h
@@ -44,10 +44,6 @@ class ExtensionSystemFactory : public BrowserContextKeyedServiceFactory {
 
   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>;
 
@@ -59,8 +55,6 @@ class ExtensionSystemFactory : public BrowserContextKeyedServiceFactory {
   virtual content::BrowserContext* GetBrowserContextToUse(
       content::BrowserContext* context) const OVERRIDE;
   virtual bool ServiceIsCreatedWithBrowserContext() const OVERRIDE;
-
-  ExtensionSystem* custom_instance_;  // Not owned.
 };
 
 }  // namespace extensions