Move Singleton and related structs to namespace base

chrome/browser/favicon/favicon_service_factory.h

Index: chrome/browser/favicon/favicon_service_factory.h
diff --git a/chrome/browser/favicon/favicon_service_factory.h b/chrome/browser/favicon/favicon_service_factory.h
index 6da30f4ffa5a0f8d3caeaf5861c21300abcddf91..ef629fe5b65410136933a66fa90b38772aba6920 100644
--- a/chrome/browser/favicon/favicon_service_factory.h
+++ b/chrome/browser/favicon/favicon_service_factory.h
@@ -8,7 +8,9 @@
 #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 Profile;
 
@@ -33,7 +35,7 @@ class FaviconServiceFactory : public BrowserContextKeyedServiceFactory {
   static TestingFactoryFunction GetDefaultFactory();
 
  private:
-  friend struct DefaultSingletonTraits<FaviconServiceFactory>;
+  friend struct base::DefaultSingletonTraits<FaviconServiceFactory>;
 
   FaviconServiceFactory();
   ~FaviconServiceFactory() override;