We should use UserID object to identify users instead of username.

chrome/browser/chromeos/login/supervised/supervised_user_login_flow.cc

Index: chrome/browser/chromeos/login/supervised/supervised_user_login_flow.cc
diff --git a/chrome/browser/chromeos/login/supervised/supervised_user_login_flow.cc b/chrome/browser/chromeos/login/supervised/supervised_user_login_flow.cc
index d47863c674ffcc01163e06bcc10521c1db5dbbee..e0b659a897c605522b378d2cbfac6221a4828cab 100644
--- a/chrome/browser/chromeos/login/supervised/supervised_user_login_flow.cc
+++ b/chrome/browser/chromeos/login/supervised/supervised_user_login_flow.cc
@@ -29,7 +29,7 @@ using content::BrowserThread;
 namespace chromeos {
 
 SupervisedUserLoginFlow::SupervisedUserLoginFlow(
-    const std::string& user_id)
+    const user_manager::UserID& user_id)
     : ExtendedUserFlow(user_id),
       data_loaded_(false),
       weak_factory_(this) {
@@ -109,7 +109,7 @@ void SupervisedUserLoginFlow::OnPasswordChangeDataLoaded(
   SupervisedUserAuthentication* auth =
       ChromeUserManager::Get()->GetSupervisedUserManager()->GetAuthentication();
   if (!auth->NeedPasswordChange(user_id(), password_data)) {
-    VLOG(1) << "Password already changed for " << user_id();
+    VLOG(1) << "Password already changed for " << user_id().GetUserEmail();
     auth->ClearScheduledPasswordUpdate(user_id());
     Finish();
     return;