ExistingUserController is used for login under automation tests.

chrome/chrome_browser.gypi

 # Copyright (c) 2011 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.
 
 {
   'targets': [
     {
       'target_name': 'browser',
       'type': '<(library)',
       'msvs_guid': '5BF908A7-68FB-4A4B-99E3-8C749F1FE4EA',
@@ skipping 575 matching lines @@
         'browser/chromeos/login/issue_response_handler.cc',
         'browser/chromeos/login/issue_response_handler.h',
         'browser/chromeos/login/keyboard_switch_menu.cc',
         'browser/chromeos/login/keyboard_switch_menu.h',
         'browser/chromeos/login/language_switch_menu.cc',
         'browser/chromeos/login/language_switch_menu.h',
         'browser/chromeos/login/login_html_dialog.cc',
         'browser/chromeos/login/login_html_dialog.h',
         'browser/chromeos/login/login_performer.cc',
         'browser/chromeos/login/login_performer.h',
-        'browser/chromeos/login/login_screen.cc',
-        'browser/chromeos/login/login_screen.h',
         'browser/chromeos/login/login_status_consumer.h',
         'browser/chromeos/login/login_utils.cc',
         'browser/chromeos/login/login_utils.h',
         'browser/chromeos/login/message_bubble.h',
         'browser/chromeos/login/message_bubble.cc',
         'browser/chromeos/login/network_selection_view.cc',
         'browser/chromeos/login/network_selection_view.h',
         'browser/chromeos/login/network_screen.cc',
         'browser/chromeos/login/network_screen.h',
         'browser/chromeos/login/network_screen_delegate.h',
@@ skipping 3950 matching lines @@
       ],
     },
   ],
 }
 
 # Local Variables:
 # tab-width:2
 # indent-tabs-mode:nil
 # End:
 # vim: set expandtab tabstop=2 shiftwidth=2: