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

chromeos/login/auth/stub_authenticator.cc

Index: chromeos/login/auth/stub_authenticator.cc
diff --git a/chromeos/login/auth/stub_authenticator.cc b/chromeos/login/auth/stub_authenticator.cc
index 6613ea2b7f4623542b9a673a1bcd7432999ae680..c3f2e5ed670e051b37a3f501d0a6d51b4318b870 100644
--- a/chromeos/login/auth/stub_authenticator.cc
+++ b/chromeos/login/auth/stub_authenticator.cc
@@ -56,7 +56,7 @@ void StubAuthenticator::AuthenticateToUnlock(const UserContext& user_context) {
 
 void StubAuthenticator::LoginAsSupervisedUser(const UserContext& user_context) {
   UserContext new_user_context = user_context;
-  new_user_context.SetUserIDHash(user_context.GetUserID() + kUserIdHashSuffix);
+  new_user_context.SetUserIDHash(user_context.GetUserID().GetUserEmail() + kUserIdHashSuffix);
   consumer_->OnAuthSuccess(new_user_context);
 }
 
@@ -67,16 +67,16 @@ void StubAuthenticator::LoginOffTheRecord() {
 void StubAuthenticator::LoginAsPublicSession(const UserContext& user_context) {
   UserContext logged_in_user_context = user_context;
   logged_in_user_context.SetIsUsingOAuth(false);
-  logged_in_user_context.SetUserIDHash(logged_in_user_context.GetUserID() +
+  logged_in_user_context.SetUserIDHash(logged_in_user_context.GetUserID().GetUserEmail() +
                                        kUserIdHashSuffix);
   consumer_->OnAuthSuccess(logged_in_user_context);
 }
 
-void StubAuthenticator::LoginAsKioskAccount(const std::string& app_user_id,
+void StubAuthenticator::LoginAsKioskAccount(const user_manager::UserID& app_user_id,
                                             bool use_guest_mount) {
   UserContext user_context(expected_user_context_.GetUserID());
   user_context.SetIsUsingOAuth(false);
-  user_context.SetUserIDHash(expected_user_context_.GetUserID() +
+  user_context.SetUserIDHash(expected_user_context_.GetUserID().GetUserEmail() +
                              kUserIdHashSuffix);
   consumer_->OnAuthSuccess(user_context);
 }
@@ -85,7 +85,7 @@ void StubAuthenticator::OnAuthSuccess() {
   // If we want to be more like the real thing, we could save the user ID
   // in AuthenticateToLogin, but there's not much of a point.
   UserContext user_context(expected_user_context_);
-  user_context.SetUserIDHash(expected_user_context_.GetUserID() +
+  user_context.SetUserIDHash(expected_user_context_.GetUserID().GetUserEmail() +
                              kUserIdHashSuffix);
   consumer_->OnAuthSuccess(user_context);
 }