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

components/user_manager/user_info_impl.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 "components/user_manager/user_info_impl.h"
 
 #include "base/logging.h"
 #include "base/strings/utf_string_conversions.h"
 
 namespace user_manager {
 
-UserInfoImpl::UserInfoImpl() {
+UserInfoImpl::UserInfoImpl() : user_id_(UserID::FromUserEmail(GetEmail())) {
 }
 
 UserInfoImpl::~UserInfoImpl() {
 }
 
 base::string16 UserInfoImpl::GetDisplayName() const {
   return base::UTF8ToUTF16("stub-user");
 }
 
 base::string16 UserInfoImpl::GetGivenName() const {
   return base::UTF8ToUTF16("Stub");
 }
 
 std::string UserInfoImpl::GetEmail() const {
   return "stub-user@domain.com";
 }
 
-std::string UserInfoImpl::GetUserID() const {
-  return GetEmail();
+const UserID& UserInfoImpl::GetUserID() const {
+  return user_id_;
 }
 
 const gfx::ImageSkia& UserInfoImpl::GetImage() const {
   return user_image_;
 }
 
 }  // namespace user_manager