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

chrome/browser/ui/ash/multi_user/multi_user_context_menu_chromeos.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/ui/ash/multi_user/multi_user_context_menu.h"
 
 #include "ash/multi_profile_uma.h"
 #include "ash/session/session_state_delegate.h"
 #include "ash/shell.h"
 #include "base/bind.h"
@@ skipping 57 matching lines @@
   ash::SessionStateDelegate* delegate =
       ash::Shell::GetInstance()->session_state_delegate();
   if (!delegate)
     return model.Pass();
 
   int logged_in_users = delegate->NumberOfLoggedInUsers();
   if (logged_in_users > 1) {
     // If this window is not owned, we don't show the menu addition.
     chrome::MultiUserWindowManager* manager =
         chrome::MultiUserWindowManager::GetInstance();
-    const std::string user_id = manager->GetWindowOwner(window);
+    const user_manager::UserID user_id = manager->GetWindowOwner(window);
     if (user_id.empty() || !window)
       return model.Pass();
     chromeos::MultiUserContextMenuChromeos* menu =
         new chromeos::MultiUserContextMenuChromeos(window);
     model.reset(menu);
     for (int user_index = 1; user_index < logged_in_users; ++user_index) {
       const user_manager::UserInfo* user_info =
           delegate->GetUserInfo(user_index);
       menu->AddItem(user_index == 1 ? IDC_VISIT_DESKTOP_OF_LRU_USER_2
                                     : IDC_VISIT_DESKTOP_OF_LRU_USER_3,
                     l10n_util::GetStringFUTF16(
                         IDS_VISIT_DESKTOP_OF_LRU_USER,
                         user_info->GetDisplayName(),
                         base::ASCIIToUTF16(user_info->GetEmail())));
     }
   }
   return model.Pass();
 }
 
 void OnAcceptTeleportWarning(
-    const std::string user_id, aura::Window* window_, bool no_show_again) {
+    const user_manager::UserID user_id, aura::Window* window_, bool no_show_again) {
   PrefService* pref = ProfileManager::GetActiveUserProfile()->GetPrefs();
   pref->SetBoolean(prefs::kMultiProfileWarningShowDismissed, no_show_again);
 
   ash::MultiProfileUMA::RecordTeleportAction(
       ash::MultiProfileUMA::TELEPORT_WINDOW_CAPTION_MENU);
 
   chrome::MultiUserWindowManager::GetInstance()->ShowWindowForUser(window_,
                                                                    user_id);
 }
 
 void ExecuteVisitDesktopCommand(int command_id, aura::Window* window) {
   switch (command_id) {
     case IDC_VISIT_DESKTOP_OF_LRU_USER_2:
     case IDC_VISIT_DESKTOP_OF_LRU_USER_3: {
       // When running the multi user mode on Chrome OS, windows can "visit"
       // another user's desktop.
-      const std::string& user_id =
+      const user_manager::UserID& user_id =
           ash::Shell::GetInstance()
               ->session_state_delegate()
               ->GetUserInfo(IDC_VISIT_DESKTOP_OF_LRU_USER_2 == command_id ? 1
                                                                           : 2)
               ->GetUserID();
       base::Callback<void(bool)> on_accept =
           base::Bind(&OnAcceptTeleportWarning, user_id, window);
 
       // Don't show warning dialog if any logged in user in multi-profiles
       // session dismissed it.
       const user_manager::UserList logged_in_users =
           user_manager::UserManager::Get()->GetLoggedInUsers();
       for (user_manager::UserList::const_iterator it = logged_in_users.begin();
            it != logged_in_users.end();
            ++it) {
         if (multi_user_util::GetProfileFromUserID(
-            multi_user_util::GetUserIDFromEmail((*it)->email()))->GetPrefs()->
+            multi_user_util::GetUserIDFromEmail((*it)->GetUserID().GetUserEmail()))->GetPrefs()->
             GetBoolean(prefs::kMultiProfileWarningShowDismissed)) {
           bool active_user_show_option =
               ProfileManager::GetActiveUserProfile()->
               GetPrefs()->GetBoolean(prefs::kMultiProfileWarningShowDismissed);
           on_accept.Run(active_user_show_option);
           return;
         }
       }
       chromeos::ShowMultiprofilesWarningDialog(on_accept);
       return;
     }
     default:
       NOTREACHED();
   }
 }