Move Singleton and related structs to namespace base

chrome/browser/chromeos/login/ui/user_adding_screen.cc

Index: chrome/browser/chromeos/login/ui/user_adding_screen.cc
diff --git a/chrome/browser/chromeos/login/ui/user_adding_screen.cc b/chrome/browser/chromeos/login/ui/user_adding_screen.cc
index 46cd6e83af55d94f61faaded46b15e9f5fabf9ab..8f6ba741d6b301aaf6daf84893c46bfbb9526099 100644
--- a/chrome/browser/chromeos/login/ui/user_adding_screen.cc
+++ b/chrome/browser/chromeos/login/ui/user_adding_screen.cc
@@ -34,7 +34,7 @@ class UserAddingScreenImpl : public UserAddingScreen {
 
   static UserAddingScreenImpl* GetInstance();
  private:
-  friend struct DefaultSingletonTraits<UserAddingScreenImpl>;
+  friend struct base::DefaultSingletonTraits<UserAddingScreenImpl>;
 
   void OnDisplayHostCompletion();
 
@@ -97,7 +97,7 @@ void UserAddingScreenImpl::OnDisplayHostCompletion() {
 
 // static
 UserAddingScreenImpl* UserAddingScreenImpl::GetInstance() {
-  return Singleton<UserAddingScreenImpl>::get();
+  return base::Singleton<UserAddingScreenImpl>::get();
 }
 
 UserAddingScreenImpl::UserAddingScreenImpl()