Move Singleton and related structs to namespace base

chrome/browser/content_settings/host_content_settings_map_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_CONTENT_SETTINGS_HOST_CONTENT_SETTINGS_MAP_FACTORY_H_
 #define CHROME_BROWSER_CONTENT_SETTINGS_HOST_CONTENT_SETTINGS_MAP_FACTORY_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/singleton.h"
 #include "components/keyed_service/content/refcounted_browser_context_keyed_service_factory.h"
 
 class HostContentSettingsMap;
 class Profile;
 
 class HostContentSettingsMapFactory
     : public RefcountedBrowserContextKeyedServiceFactory {
  public:
   static HostContentSettingsMap* GetForProfile(Profile* profile);
   static HostContentSettingsMapFactory* GetInstance();
 
  private:
-  friend struct DefaultSingletonTraits<HostContentSettingsMapFactory>;
+  friend struct base::DefaultSingletonTraits<HostContentSettingsMapFactory>;
 
   HostContentSettingsMapFactory();
   ~HostContentSettingsMapFactory() override;
 
   // RefcountedBrowserContextKeyedServiceFactory methods:
   scoped_refptr<RefcountedKeyedService> BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
   content::BrowserContext* GetBrowserContextToUse(
       content::BrowserContext* context) const override;
 
   DISALLOW_COPY_AND_ASSIGN(HostContentSettingsMapFactory);
 };
 
 #endif // CHROME_BROWSER_CONTENT_SETTINGS_HOST_CONTENT_SETTINGS_MAP_FACTORY_H_