Move Singleton and related structs to namespace base

chrome/browser/storage/durable_storage_permission_context_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 CHROME_BROWSER_STORAGE_DURABLE_STORAGE_PERMISSION_CONTEXT_FACTORY_H_
 #define CHROME_BROWSER_STORAGE_DURABLE_STORAGE_PERMISSION_CONTEXT_FACTORY_H_
 
 #include "base/memory/singleton.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
 class DurableStoragePermissionContext;
 class Profile;
 
 class DurableStoragePermissionContextFactory
     : public BrowserContextKeyedServiceFactory {
  public:
   static DurableStoragePermissionContext* GetForProfile(Profile* profile);
   static DurableStoragePermissionContextFactory* GetInstance();
 
  private:
-  friend struct DefaultSingletonTraits<DurableStoragePermissionContextFactory>;
+  friend struct base::DefaultSingletonTraits<
+      DurableStoragePermissionContextFactory>;
 
   DurableStoragePermissionContextFactory();
   ~DurableStoragePermissionContextFactory() override = default;
 
   // BrowserContextKeyedBaseFactory methods:
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* profile) const override;
   content::BrowserContext* GetBrowserContextToUse(
       content::BrowserContext* context) const override;
 
   DISALLOW_COPY_AND_ASSIGN(DurableStoragePermissionContextFactory);
 };
 
 #endif  // CHROME_BROWSER_STORAGE_DURABLE_STORAGE_PERMISSION_CONTEXT_FACTORY_H_