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

chrome/browser/chromeos/login/easy_unlock/easy_unlock_reauth.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 "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/chromeos/login/easy_unlock/easy_unlock_reauth.h"
 #include "chrome/browser/chromeos/login/lock/screen_locker.h"
 #include "chrome/browser/signin/proximity_auth_facade.h"
@@ skipping 68 matching lines @@
     icon_options.SetIcon(
         proximity_auth::ScreenlockBridge::USER_POD_CUSTOM_ICON_NONE);
     icon_options.SetTooltip(
         l10n_util::GetStringUTF16(
             IDS_SMART_LOCK_SCREENLOCK_TOOLTIP_HARDLOCK_REAUTH_USER),
         true);
 
     const user_manager::UserList& lock_users = screen_locker->users();
     DCHECK(lock_users.size() == 1);
     GetScreenlockBridgeInstance()->lock_handler()->ShowUserPodCustomIcon(
-        lock_users[0]->email(), icon_options);
+        lock_users[0]->GetUserID(), icon_options);
   }
 
   // chromeos::AuthStatusConsumer:
   void OnAuthSuccess(const chromeos::UserContext& user_context) override {
     callback_.Run(user_context);
     // Schedule deletion.
     base::MessageLoopForUI::current()->PostTask(FROM_HERE,
                                                 base::Bind(&EndReauthAttempt));
   }
 
@@ skipping 22 matching lines @@
     base::Callback<void(const UserContext&)> callback) {
   DCHECK(base::MessageLoopForUI::IsCurrent());
   if (g_reauth_handler)
     return false;
 
   g_reauth_handler = new ReauthHandler(callback);
   return g_reauth_handler->Start();
 }
 
 }  // namespace chromeos