ExistingUserController is used for login under automation tests.

chrome/chrome_tests.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.
 
 {
   'variables' : {
     'pyautolib_sources': [
       'app/chrome_command_ids.h',
       'app/chrome_dll_resource.h',
       'common/automation_constants.h',
@@ skipping 1993 matching lines @@
         'browser/chromeos/cros/mock_mount_library.cc',
         'browser/chromeos/cros/mock_mount_library.h',
         'browser/chromeos/cros/mock_network_library.h',
         'browser/chromeos/cros/mock_power_library.h',
         'browser/chromeos/cros/mock_speech_synthesis_library.h',
         'browser/chromeos/cros/mock_system_library.h',
         'browser/chromeos/cros/mock_touchpad_library.h',
         'browser/chromeos/login/account_screen_browsertest.cc',
         'browser/chromeos/login/existing_user_controller_browsertest.cc',
         'browser/chromeos/login/login_browsertest.cc',
-        'browser/chromeos/login/login_screen_browsertest.cc',
         'browser/chromeos/login/mock_authenticator.h',
         'browser/chromeos/login/network_screen_browsertest.cc',
         'browser/chromeos/login/screen_locker_browsertest.cc',
         'browser/chromeos/login/screen_locker_tester.cc',
         'browser/chromeos/login/screen_locker_tester.h',
         'browser/chromeos/login/update_screen_browsertest.cc',
         'browser/chromeos/login/wizard_controller_browsertest.cc',
         'browser/chromeos/login/wizard_in_process_browser_test.cc',
         'browser/chromeos/login/wizard_in_process_browser_test.h',
         'browser/chromeos/network_state_notifier_browsertest.cc',
@@ skipping 1611 matching lines @@
       ]
     }],  # 'coverage!=0'
   ],  # 'conditions'
 }
 
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