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

chrome/browser/chromeos/login/app_launch_signin_screen.cc

 // Copyright 2013 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/app_launch_signin_screen.h"
 
 #include "base/values.h"
 #include "chrome/browser/chromeos/login/help_app_launcher.h"
 #include "chrome/browser/chromeos/login/screens/user_selection_screen.h"
 #include "chrome/browser/chromeos/login/session/user_session_manager.h"
@@ skipping 24 matching lines @@
 void AppLaunchSigninScreen::Show() {
   InitOwnerUserList();
   oobe_ui_->web_ui()->CallJavascriptFunction(
       "login.AccountPickerScreen.setShouldShowApps",
       base::FundamentalValue(false));
   oobe_ui_->ShowSigninScreen(LoginScreenContext(), this, NULL);
 }
 
 void AppLaunchSigninScreen::InitOwnerUserList() {
   user_manager::UserManager* user_manager = GetUserManager();
-  const std::string& owner_email = user_manager->GetOwnerEmail();
+  const user_manager::UserID& owner_id = user_manager->GetOwnerID();
   const user_manager::UserList& all_users = user_manager->GetUsers();
 
   owner_user_list_.clear();
   for (user_manager::UserList::const_iterator it = all_users.begin();
        it != all_users.end();
        ++it) {
     user_manager::User* user = *it;
-    if (user->email() == owner_email) {
+    if (user->GetUserID() == owner_id) {

[Denis Kuznetsov (DE-MUC), 2015/06/10 16:50:46]

We should think about == contract for UserID, like, if one userid is (GaiaID,
someone@gmail.com) and second one is ("", someone@gmail.com) should be they
treated as same or not?
Maybe we should keep == for field-by-field equality, and have separate method
bool matches(UserID other) for "equal, even though one of elements can be
incomplete", ?

       owner_user_list_.push_back(user);
       break;
     }
   }
 }
 
 // static
 void AppLaunchSigninScreen::SetUserManagerForTesting(
     user_manager::UserManager* user_manager) {
   test_user_manager_ = user_manager;
@@ skipping 29 matching lines @@
       content::BrowserThread::UI, FROM_HERE,
       base::Bind(&Authenticator::AuthenticateToUnlock,
                  authenticator_.get(),
                  user_context));
 }
 
 void AppLaunchSigninScreen::MigrateUserData(const std::string& old_password) {
   NOTREACHED();
 }
 
-void AppLaunchSigninScreen::LoadWallpaper(const std::string& username) {
+void AppLaunchSigninScreen::LoadWallpaper(const user_manager::UserID& user_id) {
 }
 
 void AppLaunchSigninScreen::LoadSigninWallpaper() {
 }
 
 void AppLaunchSigninScreen::OnSigninScreenReady() {
 }
 
-void AppLaunchSigninScreen::RemoveUser(const std::string& username) {
+void AppLaunchSigninScreen::RemoveUser(const user_manager::UserID& user_id) {
   NOTREACHED();
 }
 
 void AppLaunchSigninScreen::ResyncUserData() {
   NOTREACHED();
 }
 
 void AppLaunchSigninScreen::ShowEnterpriseEnrollmentScreen() {
   NOTREACHED();
 }
@@ skipping 13 matching lines @@
 void AppLaunchSigninScreen::ShowWrongHWIDScreen() {
   NOTREACHED();
 }
 
 void AppLaunchSigninScreen::SetWebUIHandler(
     LoginDisplayWebUIHandler* webui_handler) {
   webui_handler_ = webui_handler;
 }
 
 void AppLaunchSigninScreen::ShowSigninScreenForCreds(
-    const std::string& username,
+    const user_manager::UserID& user_id,
     const std::string& password) {
   NOTREACHED();
 }
 
 const user_manager::UserList& AppLaunchSigninScreen::GetUsers() const {
   if (test_user_manager_) {
     return test_user_manager_->GetUsers();
   }
   return owner_user_list_;
 }
@@ skipping 53 matching lines @@
         false,  /* is_signin_to_add */
         initial_auth_type,
         NULL,   /* public_session_recommended_locales */
         user_dict);
     users_list.Append(user_dict);
   }
 
   webui_handler_->LoadUsers(users_list, false);
 }
 
-void AppLaunchSigninScreen::CheckUserStatus(const std::string& user_id) {
+void AppLaunchSigninScreen::CheckUserStatus(const user_manager::UserID& user_id) {
 }
 
 }  // namespace chromeos