Move Singleton and related structs to namespace base

chrome/browser/extensions/extension_garbage_collector_factory.h

 // Copyright 2014 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_GARBAGE_COLLECTOR_FACTORY_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_GARBAGE_COLLECTOR_FACTORY_H_
 
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
+namespace base {
 template <typename T>
 struct DefaultSingletonTraits;
+}
 
 class Profile;
 
 namespace extensions {
 
 class ExtensionGarbageCollector;
 
 class ExtensionGarbageCollectorFactory
     : public BrowserContextKeyedServiceFactory {
  public:
   static ExtensionGarbageCollector* GetForBrowserContext(
       content::BrowserContext* context);
 
   static ExtensionGarbageCollectorFactory* GetInstance();
 
   static scoped_ptr<KeyedService> BuildInstanceFor(
       content::BrowserContext* context);
 
  private:
-  friend struct DefaultSingletonTraits<ExtensionGarbageCollectorFactory>;
+  friend struct base::DefaultSingletonTraits<ExtensionGarbageCollectorFactory>;
 
   ExtensionGarbageCollectorFactory();
   ~ExtensionGarbageCollectorFactory() override;
 
   // BrowserContextKeyedServiceFactory overrides:
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
 
   bool ServiceIsCreatedWithBrowserContext() const override;
   bool ServiceIsNULLWhileTesting() const override;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionGarbageCollectorFactory);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_GARBAGE_COLLECTOR_FACTORY_H_