Move Singleton and related structs to namespace base

chrome/browser/apps/per_app_settings_service_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_APPS_PER_APP_SETTINGS_SERVICE_FACTORY_H_
 #define CHROME_BROWSER_APPS_PER_APP_SETTINGS_SERVICE_FACTORY_H_
 
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
 namespace content {
 class BrowserContext;
 }
 
 class PerAppSettingsService;
 
+namespace base {
 template <typename T> struct DefaultSingletonTraits;
+}
+
 class PerAppSettingsServiceFactory : public BrowserContextKeyedServiceFactory {
  public:
   static PerAppSettingsServiceFactory* GetInstance();
   static PerAppSettingsService* GetForBrowserContext(
       content::BrowserContext* browser_context);
 
  private:
-  friend struct DefaultSingletonTraits<PerAppSettingsServiceFactory>;
+  friend struct base::DefaultSingletonTraits<PerAppSettingsServiceFactory>;
 
   PerAppSettingsServiceFactory();
   ~PerAppSettingsServiceFactory() override;
 
   // BrowserContextKeyedServiceFactory:
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
   bool ServiceIsCreatedWithBrowserContext() const override;
   content::BrowserContext* GetBrowserContextToUse(
       content::BrowserContext* context) const override;
 };
 
 #endif  // CHROME_BROWSER_APPS_PER_APP_SETTINGS_SERVICE_FACTORY_H_