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

chrome/browser/chromeos/login/chrome_restart_request.cc

 // Copyright 2013 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/chrome_restart_request.h"
 
 #include <vector>
 
 #include "ash/ash_switches.h"
 #include "base/command_line.h"
@@ skipping 13 matching lines @@
 #include "chrome/browser/lifetime/application_lifetime.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/url_constants.h"
 #include "chromeos/chromeos_switches.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #include "chromeos/dbus/session_manager_client.h"
 #include "chromeos/login/user_names.h"
 #include "components/policy/core/common/policy_switches.h"
+#include "components/user_manager/user_id.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/common/content_switches.h"
 #include "gpu/command_buffer/service/gpu_switches.h"
 #include "media/base/media_switches.h"
 #include "third_party/cros_system_api/switches/chrome_switches.h"
 #include "ui/app_list/app_list_switches.h"
 #include "ui/base/ui_base_switches.h"
 #include "ui/compositor/compositor_switches.h"
 #include "ui/events/event_switches.h"
 #include "ui/gfx/switches.h"
@@ skipping 292 matching lines @@
 
 std::string GetOffTheRecordCommandLine(
     const GURL& start_url,
     bool is_oobe_completed,
     const base::CommandLine& base_command_line,
     base::CommandLine* command_line) {
   base::DictionaryValue otr_switches;
   otr_switches.SetString(switches::kGuestSession, std::string());
   otr_switches.SetString(::switches::kIncognito, std::string());
   otr_switches.SetString(::switches::kLoggingLevel, kGuestModeLoggingLevel);
-  otr_switches.SetString(switches::kLoginUser, chromeos::login::kGuestUserName);
+  otr_switches.SetString(switches::kLoginUser, chromeos::login::GetGuestUserID().GetUserEmail());
 
   // Override the home page.
   otr_switches.SetString(::switches::kHomePage,
                          GURL(chrome::kChromeUINewTabURL).spec());
 
   // If OOBE is not finished yet, lock down the guest session to not allow
   // surfing the web. Guest mode is still useful to inspect logs and run network
   // diagnostics.
   if (!is_oobe_completed)
     otr_switches.SetString(switches::kOobeGuestSession, std::string());
@@ skipping 18 matching lines @@
     // Relaunch chrome without session manager on dev box.
     ReLaunch(command_line);
     return;
   }
 
   // ChromeRestartRequest deletes itself after request sent to session manager.
   (new ChromeRestartRequest(command_line))->Start();
 }
 
 }  // namespace chromeos