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

chrome/browser/chromeos/login/easy_unlock/easy_unlock_user_login_flow.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/easy_unlock/easy_unlock_user_login_flow.h"
 
 #include "chrome/browser/chromeos/profiles/profile_helper.h"
 #include "chrome/browser/signin/easy_unlock_service.h"
 
-EasyUnlockUserLoginFlow::EasyUnlockUserLoginFlow(const std::string& user_id)
+EasyUnlockUserLoginFlow::EasyUnlockUserLoginFlow(const user_manager::UserID& user_id)
     : chromeos::ExtendedUserFlow(user_id) {
 }
 
 EasyUnlockUserLoginFlow::~EasyUnlockUserLoginFlow() {}
 
 bool EasyUnlockUserLoginFlow::CanLockScreen() {
   return true;
 }
 
 bool EasyUnlockUserLoginFlow::ShouldLaunchBrowser() {
@@ skipping 32 matching lines @@
 void EasyUnlockUserLoginFlow::HandleOAuthTokenStatusChange(
     user_manager::User::OAuthTokenStatus status) {
 }
 
 void EasyUnlockUserLoginFlow::LaunchExtraSteps(Profile* profile) {
 }
 
 bool EasyUnlockUserLoginFlow::SupportsEarlyRestartToApplyFlags() {
   return true;
 }