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

chrome/browser/chromeos/login/screens/error_screen.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/login/screens/error_screen.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/logging.h"
@@ skipping 222 matching lines @@
                                  browser_command_line,
                                  &command_line);
 
   RestartChrome(cmd_line_str);
 }
 
 void ErrorScreen::OnPasswordChangeDetected() {
   LOG(FATAL);
 }
 
-void ErrorScreen::WhiteListCheckFailed(const std::string& email) {
+void ErrorScreen::WhiteListCheckFailed(const user_manager::UserID& user_id) {
   LOG(FATAL);
 }
 
 void ErrorScreen::PolicyLoadFailed() {
   LOG(FATAL);
 }
 
-void ErrorScreen::OnOnlineChecked(const std::string& username, bool success) {
+void ErrorScreen::OnOnlineChecked(const user_manager::UserID& user_id, bool success) {
   LOG(FATAL);
 }
 
 void ErrorScreen::DefaultHideCallback() {
   if (parent_screen_ != OobeUI::SCREEN_UNKNOWN && view_)
     view_->ShowScreen(parent_screen_);
 
   // TODO(antrim): Due to potential race with GAIA reload and hiding network
   // error UI we can't just reset parent screen to SCREEN_UNKNOWN here.
 }
@@ skipping 72 matching lines @@
   }
 
   if (guest_login_performer_)
     return;
 
   guest_login_performer_.reset(new ChromeLoginPerformer(this));
   guest_login_performer_->LoginOffTheRecord();
 }
 
 }  // namespace chromeos