Move Singleton and related structs to namespace base

ios/chrome/browser/signin/account_consistency_service_factory.h

 // Copyright 2015 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 IOS_CHROME_BROWSER_SIGNIN_ACCOUNT_CONSISTENCY_SERVICE_FACTORY_H_
 #define IOS_CHROME_BROWSER_SIGNIN_ACCOUNT_CONSISTENCY_SERVICE_FACTORY_H_
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "components/keyed_service/ios/browser_state_keyed_service_factory.h"
 
+namespace base {
 template <typename T>
 struct DefaultSingletonTraits;
+}
+
 class AccountConsistencyService;
 
 namespace ios {
 
 class ChromeBrowserState;
 
 // Singleton that owns the AccountConsistencyService(s) and associates them with
 // browser states.
 class AccountConsistencyServiceFactory
     : public BrowserStateKeyedServiceFactory {
  public:
   // Returns the instance of AccountConsistencyService associated with this
   // browser state (creating one if none exists). Returns null if this browser
   // state cannot have an AccountConsistencyService (for example, if it is
   // incognito or if WKWebView is not enabled).
   static AccountConsistencyService* GetForBrowserState(
       ios::ChromeBrowserState* browser_state);
 
   // Returns an instance of the factory singleton.
   static AccountConsistencyServiceFactory* GetInstance();
 
  private:
-  friend struct DefaultSingletonTraits<AccountConsistencyServiceFactory>;
+  friend struct base::DefaultSingletonTraits<AccountConsistencyServiceFactory>;
 
   AccountConsistencyServiceFactory();
   ~AccountConsistencyServiceFactory() override;
 
   // BrowserStateKeyedServiceFactory:
   scoped_ptr<KeyedService> BuildServiceInstanceFor(
       web::BrowserState* context) const override;
   bool ServiceIsCreatedWithBrowserState() const override;
 
   DISALLOW_COPY_AND_ASSIGN(AccountConsistencyServiceFactory);
 };
 
 }  // namespace ios
 
 #endif  // IOS_CHROME_BROWSER_SIGNIN_ACCOUNT_CONSISTENCY_SERVICE_FACTORY_H_