Move Singleton and related structs to namespace base

extensions/browser/extension_registry_factory.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 EXTENSIONS_BROWSER_EXTENSION_REGISTRY_FACTORY_H_
 #define EXTENSIONS_BROWSER_EXTENSION_REGISTRY_FACTORY_H_
 
 #include "base/compiler_specific.h"
 #include "base/memory/singleton.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
 namespace extensions {
 
 class ExtensionRegistry;
 
 // Factory for ExtensionRegistry objects. ExtensionRegistry objects are shared
 // between an incognito browser context and its master browser context.
 class ExtensionRegistryFactory : public BrowserContextKeyedServiceFactory {
  public:
   static ExtensionRegistry* GetForBrowserContext(
       content::BrowserContext* context);
 
   static ExtensionRegistryFactory* GetInstance();
 
  private:
-  friend struct DefaultSingletonTraits<ExtensionRegistryFactory>;
+  friend struct base::DefaultSingletonTraits<ExtensionRegistryFactory>;
 
   ExtensionRegistryFactory();
   ~ExtensionRegistryFactory() override;
 
   // BrowserContextKeyedServiceFactory implementation:
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
   content::BrowserContext* GetBrowserContextToUse(
       content::BrowserContext* context) const override;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionRegistryFactory);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_EXTENSION_REGISTRY_FACTORY_H_