UMA to track the reason for re-auth

chrome/chrome_browser_chromeos.gypi

 # 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.
 
 {
   'variables': {
     # These files lists are shared with the GN build.
     'browser_chromeos_sources': [
         # All .cc, .h, .m, and .mm files under browser/chromeos, except for tests
@@ skipping 484 matching lines @@
         'browser/chromeos/login/lock/webui_screen_locker.cc',
         'browser/chromeos/login/lock/webui_screen_locker.h',
         'browser/chromeos/login/login_wizard.h',
         'browser/chromeos/login/profile_auth_data.cc',
         'browser/chromeos/login/profile_auth_data.h',
         'browser/chromeos/login/proxy_settings_dialog.h',
         'browser/chromeos/login/saml/saml_offline_signin_limiter.cc',
         'browser/chromeos/login/saml/saml_offline_signin_limiter.h',
         'browser/chromeos/login/saml/saml_offline_signin_limiter_factory.cc',
         'browser/chromeos/login/saml/saml_offline_signin_limiter_factory.h',
+        'browser/chromeos/login/reauth_stats.cc',
+        'browser/chromeos/login/reauth_stats.h',
         'browser/chromeos/login/screen_manager.cc',
         'browser/chromeos/login/screen_manager.h',
         'browser/chromeos/login/screens/base_screen.cc',
         'browser/chromeos/login/screens/base_screen.h',
         'browser/chromeos/login/screens/base_screen_delegate.h',
         'browser/chromeos/login/screens/chrome_user_selection_screen.cc',
         'browser/chromeos/login/screens/chrome_user_selection_screen.h',
         'browser/chromeos/login/screens/controller_pairing_screen.cc',
         'browser/chromeos/login/screens/controller_pairing_screen.h',
         'browser/chromeos/login/screens/controller_pairing_screen_actor.cc',
@@ skipping 816 matching lines @@
         'browser/chromeos/attestation/attestation_signed_data.proto',
       ],
       'variables': {
         'proto_in_dir': 'browser/chromeos/attestation',
         'proto_out_dir': 'chrome/browser/chromeos/attestation',
       },
       'includes': [ '../build/protoc.gypi' ]
     },
   ],
 }