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

chrome/browser/supervised_user/chromeos/supervised_user_password_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/chromeos/supervised_user_password_service.h"
 
 #include "base/bind.h"
 #include "base/values.h"
 #include "chrome/browser/chromeos/login/supervised/supervised_user_authentication.h"
 #include "chrome/browser/chromeos/login/users/chrome_user_manager.h"
 #include "chrome/browser/chromeos/login/users/supervised_user_manager.h"
 #include "chrome/browser/supervised_user/legacy/supervised_user_sync_service.h"
 #include "chrome/browser/supervised_user/supervised_user_constants.h"
+#include "components/user_manager/user_id.h"
 
 namespace chromeos {
 
 SupervisedUserPasswordService::SupervisedUserPasswordService()
-    : weak_ptr_factory_(this) {}
+    : user_id_(std::string(), std::string()), weak_ptr_factory_(this) {}
 
 SupervisedUserPasswordService::~SupervisedUserPasswordService() {}
 
 void SupervisedUserPasswordService::Init(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     SupervisedUserSharedSettingsService* shared_settings_service) {
   user_id_ = user_id;
   settings_service_ = shared_settings_service;
   settings_service_subscription_ = settings_service_->Subscribe(
       base::Bind(&SupervisedUserPasswordService::OnSharedSettingsChange,
                  weak_ptr_factory_.GetWeakPtr()));
 
   // Force value check in case we have missed some notification.
 
   chromeos::SupervisedUserManager* supervised_user_manager =
       ChromeUserManager::Get()->GetSupervisedUserManager();
 
   OnSharedSettingsChange(supervised_user_manager->GetUserSyncId(user_id),
                          supervised_users::kChromeOSPasswordData);
 }
 
 void SupervisedUserPasswordService::OnSharedSettingsChange(
     const std::string& su_id,
     const std::string& key) {
   if (key != supervised_users::kChromeOSPasswordData)
     return;
   chromeos::SupervisedUserManager* supervised_user_manager =
       ChromeUserManager::Get()->GetSupervisedUserManager();
   const user_manager::User* user = supervised_user_manager->FindBySyncId(su_id);
   if (user == NULL) {
     LOG(WARNING) << "Got notification for user not on device.";
     return;
   }
-  DCHECK(user_id_ == user->email());
-  if (user_id_ != user->email())
+  DCHECK(user_id_ == user->GetUserID());
+  if (user_id_ != user->GetUserID())
     return;
   const base::Value* value = settings_service_->GetValue(su_id, key);
   if (value == NULL) {
     LOG(WARNING) << "Got empty value from sync.";
     return;
   }
   const base::DictionaryValue* dict;
   if (!value->GetAsDictionary(&dict)) {
     LOG(WARNING) << "Got non-dictionary value from sync.";
     return;
   }
   chromeos::SupervisedUserAuthentication* auth =
       supervised_user_manager->GetAuthentication();
   if (!auth->NeedPasswordChange(user_id_, dict))
     return;
   auth->ScheduleSupervisedPasswordChange(user_id_, dict);
 }
 
 void SupervisedUserPasswordService::Shutdown() {
     settings_service_subscription_.reset();
 }
 
 }  // namespace chromeos