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

chrome/browser/chromeos/login/screens/user_image_screen.cc

 // Copyright (c) 2012 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/screens/user_image_screen.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 209 matching lines @@
 void UserImageScreen::PrepareToShow() {
   if (view_)
     view_->PrepareToShow();
 }
 
 const user_manager::User* UserImageScreen::GetUser() {
   return user_manager::UserManager::Get()->GetLoggedInUser();
 }
 
 UserImageManager* UserImageScreen::GetUserImageManager() {
-  return ChromeUserManager::Get()->GetUserImageManager(GetUser()->email());
+  return ChromeUserManager::Get()->GetUserImageManager(GetUser()->GetUserID());
 }
 
 UserImageSyncObserver* UserImageScreen::GetSyncObserver() {
   return GetUserImageManager()->GetSyncObserver();
 }
 
 void UserImageScreen::Show() {
   if (!view_)
     return;
 
@@ skipping 112 matching lines @@
 
 void UserImageScreen::ReportSyncResult(SyncResult timed_out) const {
   base::TimeDelta duration = base::Time::Now() - sync_waiting_start_time_;
   UMA_HISTOGRAM_TIMES("Login.NewUserPriorityPrefsSyncTime", duration);
   UMA_HISTOGRAM_ENUMERATION("Login.NewUserPriorityPrefsSyncResult",
                             static_cast<int>(timed_out),
                             static_cast<int>(SyncResult::COUNT));
 }
 
 }  // namespace chromeos