[Signin Error Dialog] (3/3) Added the triggering code

chrome/chrome_browser_ui.gypi

 # Copyright 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': {
     # There are two sections of sources:
     # * "Platform"-based sources (OS, toolkit, etc.)
     # * Feature/directory-based sources (e.g., history, printing)
 
@@ skipping 1375 matching lines @@
       'browser/ui/webui/settings/system_handler.cc',
       'browser/ui/webui/settings/system_handler.h',
       'browser/ui/webui/signin/inline_login_handler.cc',
       'browser/ui/webui/signin/inline_login_handler.h',
       'browser/ui/webui/signin/inline_login_handler_impl.cc',
       'browser/ui/webui/signin/inline_login_handler_impl.h',
       'browser/ui/webui/signin/inline_login_ui.cc',
       'browser/ui/webui/signin/inline_login_ui.h',
       'browser/ui/webui/signin/md_user_manager_ui.cc',
       'browser/ui/webui/signin/md_user_manager_ui.h',
+      'browser/ui/webui/signin/signin_error_handler.cc',
+      'browser/ui/webui/signin/signin_error_handler.h',
+      'browser/ui/webui/signin/signin_error_ui.cc',
+      'browser/ui/webui/signin/signin_error_ui.h',
       'browser/ui/webui/signin/signin_create_profile_handler.cc',
       'browser/ui/webui/signin/signin_create_profile_handler.h',
       'browser/ui/webui/signin/signin_supervised_user_import_handler.cc',
       'browser/ui/webui/signin/signin_supervised_user_import_handler.h',
       'browser/ui/webui/signin/sync_confirmation_handler.cc',
       'browser/ui/webui/signin/sync_confirmation_handler.h',
       'browser/ui/webui/signin/sync_confirmation_ui.cc',
       'browser/ui/webui/signin/sync_confirmation_ui.h',
       'browser/ui/webui/signin/user_manager_screen_handler.cc',
       'browser/ui/webui/signin/user_manager_screen_handler.h',
@@ skipping 1977 matching lines @@
           ],
           'sources': [
             '<@(chrome_browser_ui_non_mobile_sources)',
             '<@(chrome_browser_ui_omnibox_non_mobile_sources)',
           ],
         }],
       ],
     },
   ],
 }