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

chrome/browser/ui/ash/multi_user/multi_user_util.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_util.h"
 
 #include <vector>
 
 #include "base/strings/string_util.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_manager.h"
+#include "components/user_manager/user_id.h"
 #include "google_apis/gaia/gaia_auth_util.h"
 
 #if defined(OS_CHROMEOS)
 #include "chrome/browser/ui/ash/multi_user/multi_user_window_manager.h"
 #include "components/user_manager/user_manager.h"
 #endif
 
 namespace multi_user_util {
 
-std::string GetUserIDFromProfile(Profile* profile) {
+user_manager::UserID GetUserIDFromProfile(Profile* profile) {
   return GetUserIDFromEmail(
       profile->GetOriginalProfile()->GetProfileUserName());
 }
 
-std::string GetUserIDFromEmail(const std::string& email) {
+user_manager::UserID GetUserIDFromEmail(const std::string& email) {
   // |email| and profile name could be empty if not yet logged in or guest mode.
-  return email.empty() ?
-      email : gaia::CanonicalizeEmail(gaia::SanitizeEmail(email));
+  return user_manager::UserID::FromUserEmail(email.empty() ?
+      email : gaia::CanonicalizeEmail(gaia::SanitizeEmail(email)));
 }
 
-Profile* GetProfileFromUserID(const std::string& user_id) {
+Profile* GetProfileFromUserID(const user_manager::UserID& user_id) {
   // Unit tests can end up here without a |g_browser_process|.
   if (!g_browser_process || !g_browser_process->profile_manager())
     return NULL;
 
   std::vector<Profile*> profiles =
       g_browser_process->profile_manager()->GetLoadedProfiles();
 
   std::vector<Profile*>::const_iterator profile_iterator = profiles.begin();
   for (; profile_iterator != profiles.end(); ++profile_iterator) {
     if (GetUserIDFromProfile(*profile_iterator) == user_id)
       return *profile_iterator;
   }
   return NULL;
 }
 
 Profile* GetProfileFromWindow(aura::Window* window) {
 #if defined(OS_CHROMEOS)
   chrome::MultiUserWindowManager* manager =
       chrome::MultiUserWindowManager::GetInstance();
   // We might come here before the manager got created - or in a unit test.
   if (!manager)
     return NULL;
-  const std::string user_id = manager->GetUserPresentingWindow(window);
+  const user_manager::UserID user_id = manager->GetUserPresentingWindow(window);
   return user_id.empty() ? NULL :
                            multi_user_util::GetProfileFromUserID(user_id);
 #else
   return NULL;
 #endif
 }
 
 bool IsProfileFromActiveUser(Profile* profile) {
 #if defined(OS_CHROMEOS)
   return GetUserIDFromProfile(profile) ==
-         user_manager::UserManager::Get()->GetActiveUser()->email();
+         user_manager::UserManager::Get()->GetActiveUser()->GetUserID();
 #else
   // In non Chrome OS configurations this will be always true since this only
   // makes sense in separate desktop mode.
   return true;
 #endif
 }
 
-const std::string& GetCurrentUserId() {
+const user_manager::UserID& GetCurrentUserId() {
 #if defined(OS_CHROMEOS)
-  return user_manager::UserManager::Get()->GetActiveUser()->email();
+  return user_manager::UserManager::Get()->GetActiveUser()->GetUserID();
 #else
-  return base::EmptyString();
+  return user_manager::UserID(std::string(), std::string());
 #endif
 }
 
 // Move the window to the current user's desktop.
 void MoveWindowToCurrentDesktop(aura::Window* window) {
 #if defined(OS_CHROMEOS)
   chrome::MultiUserWindowManager::GetInstance()->ShowWindowForUser(
       window,
       GetCurrentUserId());
 #endif
 }
 
 }  // namespace multi_user_util