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

chrome/browser/supervised_user/supervised_user_service.cc

 // Copyright 2014 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/supervised_user/supervised_user_service.h"
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/memory/ref_counted.h"
@@ skipping 315 matching lines @@
 }
 
 std::string SupervisedUserService::GetCustodianEmailAddress() const {
   std::string custodian_email = profile_->GetPrefs()->GetString(
       prefs::kSupervisedUserCustodianEmail);
 #if defined(OS_CHROMEOS)
   if (custodian_email.empty()) {
     custodian_email = chromeos::ChromeUserManager::Get()
         ->GetSupervisedUserManager()
         ->GetManagerDisplayEmail(
-            user_manager::UserManager::Get()->GetActiveUser()->email());
+            user_manager::UserManager::Get()->GetActiveUser()->GetUserID());
   }
 #endif
   return custodian_email;
 }
 
 std::string SupervisedUserService::GetCustodianName() const {
   std::string name = profile_->GetPrefs()->GetString(
       prefs::kSupervisedUserCustodianName);
 #if defined(OS_CHROMEOS)
   if (name.empty()) {
     name = base::UTF16ToUTF8(chromeos::ChromeUserManager::Get()
         ->GetSupervisedUserManager()
         ->GetManagerDisplayName(
-            user_manager::UserManager::Get()->GetActiveUser()->email()));
+            user_manager::UserManager::Get()->GetActiveUser()->GetUserID()));
   }
 #endif
   return name.empty() ? GetCustodianEmailAddress() : name;
 }
 
 std::string SupervisedUserService::GetSecondCustodianEmailAddress() const {
   return profile_->GetPrefs()->GetString(
       prefs::kSupervisedUserSecondCustodianEmail);
 }
 
@@ skipping 481 matching lines @@
     // TODO(bauerb): Get rid of the platform-specific #ifdef here.
     // http://crbug.com/313377
     BrowserList::RemoveObserver(this);
 #endif
   }
 }
 
 void SupervisedUserService::RegisterAndInitSync(
     SupervisedUserRegistrationUtility* registration_utility,
     Profile* custodian_profile,
-    const std::string& supervised_user_id,
+    const user_manager::UserID& supervised_user_id,
     const AuthErrorCallback& callback) {
   DCHECK(ProfileIsSupervised());
   DCHECK(!custodian_profile->IsSupervised());
 
   base::string16 name = base::UTF8ToUTF16(
       profile_->GetPrefs()->GetString(prefs::kProfileName));
   int avatar_index = profile_->GetPrefs()->GetInteger(
       prefs::kProfileAvatarIndex);
   SupervisedUserRegistrationInfo info(name, avatar_index);
   registration_utility->Register(
@@ skipping 91 matching lines @@
   // The active user can be NULL in unit tests.
   if (user_manager::UserManager::Get()->GetActiveUser()) {
     return UTF16ToUTF8(user_manager::UserManager::Get()->GetUserDisplayName(
         user_manager::UserManager::Get()->GetActiveUser()->GetUserID()));
   }
   return std::string();
 #else
   return profile_->GetPrefs()->GetString(prefs::kProfileName);
 #endif
 }