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

chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc

Index: chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc
diff --git a/chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc b/chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc
index e0523daaa94c3956972a3bb755988cd95525c5e1..9f0ae2a38ff826ea84128485f332f464cb150e6c 100644
--- a/chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc
@@ -834,9 +834,11 @@ void GaiaScreenHandler::LoadAuthExtension(bool force,
   context.is_enrolling_consumer_management = is_enrolling_consumer_management_;
 
   std::string gaia_id;
-  if (user_manager::UserManager::Get()->FindGaiaID(
-          AccountId::FromUserEmail(context.email), &gaia_id))
+  if (!context.email.empty() &&
+      user_manager::UserManager::Get()->FindGaiaID(
+          AccountId::FromUserEmail(context.email), &gaia_id)) {
     context.gaia_id = gaia_id;
+  }
 
   if (Delegate()) {
     context.show_users = Delegate()->IsShowUsers();