This CL replaces e-mail with AccountId on user selection screen.

chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.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/ui/webui/chromeos/login/gaia_screen_handler.h"
 
 #include "ash/system/chromeos/devicetype_utils.h"
 #include "base/bind.h"
 #include "base/guid.h"
 #include "base/logging.h"
@@ skipping 816 matching lines @@
   VLOG(1) << "LoadAuthExtension, force: " << force
           << ", offline: " << offline;
   GaiaContext context;
   context.force_reload = force;
   context.is_local = offline;
   context.use_offline = offline;
   context.email = populated_email_;
   context.is_enrolling_consumer_management = is_enrolling_consumer_management_;
 
   std::string gaia_id;
-  if (user_manager::UserManager::Get()->FindGaiaID(
+  if (!context.email.empty() &&
+      user_manager::UserManager::Get()->FindGaiaID(
           AccountId::FromUserEmail(context.email), &gaia_id))
     context.gaia_id = gaia_id;

[stevenjb, 2015/11/11 20:39:23]

nit: Add {} while you're in here.

[Alexander Alekseev, 2015/11/12 06:53:04]

Done.

 
   if (Delegate()) {
     context.show_users = Delegate()->IsShowUsers();
   }
 
   if (!context.email.empty()) {
     context.gaps_cookie =
         user_manager::UserManager::Get()->GetKnownUserGAPSCookie(
             AccountId::FromUserEmail(gaia::CanonicalizeEmail(context.email)));
   }
@@ skipping 15 matching lines @@
 bool GaiaScreenHandler::IsRestrictiveProxy() const {
   return !disable_restrictive_proxy_check_for_test_ &&
          !IsOnline(captive_portal_status_);
 }
 
 void GaiaScreenHandler::DisableRestrictiveProxyCheckForTest() {
   disable_restrictive_proxy_check_for_test_ = true;
 }
 
 }  // namespace chromeos