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

chrome/browser/chromeos/login/auth/chrome_login_performer.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/chromeos/login/auth/chrome_login_performer.h"
 
 #include "base/bind.h"
 #include "base/thread_task_runner_handle.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chromeos/login/easy_unlock/easy_unlock_user_login_flow.h"
@@ skipping 68 matching lines @@
   } else if (status == CrosSettingsProvider::TEMPORARILY_UNTRUSTED) {
     // Value of AllowNewUser setting is still not verified.
     // Another attempt will be invoked after verification completion.
     return;
   } else {
     DCHECK(status == CrosSettingsProvider::TRUSTED);
     callback.Run();
   }
 }
 
-bool ChromeLoginPerformer::IsUserWhitelisted(const std::string& user_id,
+bool ChromeLoginPerformer::IsUserWhitelisted(const user_manager::UserID& user_id,
                                              bool* wildcard_match) {
   return CrosSettings::IsWhitelisted(user_id, wildcard_match);
 }
 
 void ChromeLoginPerformer::RunOnlineWhitelistCheck(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     bool wildcard_match,
     const std::string& refresh_token,
     const base::Closure& success_callback,
     const base::Closure& failure_callback) {
   // On enterprise devices, reconfirm login permission with the server.
   policy::BrowserPolicyConnectorChromeOS* connector =
       g_browser_process->platform_part()->browser_policy_connector_chromeos();
   if (connector->IsEnterpriseManaged() && wildcard_match &&
       !connector->IsNonEnterpriseUser(user_id)) {
     wildcard_login_checker_.reset(new policy::WildcardLoginChecker());
@@ skipping 31 matching lines @@
          SupervisedUserAuthentication::SCHEMA_SALT_HASHED;
 }
 
 UserContext ChromeLoginPerformer::TransformSupervisedKey(
     const UserContext& context) {
   SupervisedUserAuthentication* authentication =
       ChromeUserManager::Get()->GetSupervisedUserManager()->GetAuthentication();
   return authentication->TransformKey(context);
 }
 
-void ChromeLoginPerformer::SetupSupervisedUserFlow(const std::string& user_id) {
+void ChromeLoginPerformer::SetupSupervisedUserFlow(const user_manager::UserID& user_id) {
   SupervisedUserLoginFlow* new_flow = new SupervisedUserLoginFlow(user_id);
   new_flow->SetHost(ChromeUserManager::Get()->GetUserFlow(user_id)->host());
   ChromeUserManager::Get()->SetUserFlow(user_id, new_flow);
 }
 
-void ChromeLoginPerformer::SetupEasyUnlockUserFlow(const std::string& user_id) {
+void ChromeLoginPerformer::SetupEasyUnlockUserFlow(const user_manager::UserID& user_id) {
   ChromeUserManager::Get()->SetUserFlow(user_id,
                                         new EasyUnlockUserLoginFlow(user_id));
 }
 
-bool ChromeLoginPerformer::CheckPolicyForUser(const std::string& user_id) {
+bool ChromeLoginPerformer::CheckPolicyForUser(const user_manager::UserID& user_id) {
   // Login is not allowed if policy could not be loaded for the account.
   policy::BrowserPolicyConnectorChromeOS* connector =
       g_browser_process->platform_part()->browser_policy_connector_chromeos();
   policy::DeviceLocalAccountPolicyService* policy_service =
       connector->GetDeviceLocalAccountPolicyService();
   return policy_service && policy_service->IsPolicyAvailableForUser(user_id);
 }
 ////////////////////////////////////////////////////////////////////////////////
 // ChromeLoginPerformer, private:
 
@@ skipping 10 matching lines @@
     const base::Closure& failure_callback,
     policy::WildcardLoginChecker::Result result) {
   if (result == policy::WildcardLoginChecker::RESULT_ALLOWED) {
     success_callback.Run();
   } else {
     failure_callback.Run();
   }
 }
 
 }  // namespace chromeos