Move Singleton and related structs to namespace base

chrome/browser/web_data_service_factory.h

Index: chrome/browser/web_data_service_factory.h
diff --git a/chrome/browser/web_data_service_factory.h b/chrome/browser/web_data_service_factory.h
index 23565ebc0bbf19ccb0d3763d2b796c5435d3540e..d1b5608126275137c31d50b6d6eb5edae0890cb8 100644
--- a/chrome/browser/web_data_service_factory.h
+++ b/chrome/browser/web_data_service_factory.h
@@ -10,7 +10,10 @@
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 #include "components/keyed_service/core/service_access_type.h"
 
+namespace base {
 template <typename T> struct DefaultSingletonTraits;
+}
+
 class KeywordWebDataService;
 class Profile;
 class TokenWebData;
@@ -60,7 +63,7 @@ class WebDataServiceFactory : public BrowserContextKeyedServiceFactory {
   static WebDataServiceFactory* GetInstance();
 
  private:
-  friend struct DefaultSingletonTraits<WebDataServiceFactory>;
+  friend struct base::DefaultSingletonTraits<WebDataServiceFactory>;
 
   WebDataServiceFactory();
   ~WebDataServiceFactory() override;