Proof of concept of ignoring x-frame-options for sign-in webui.

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.
 
 {
   'targets': [
     {
       'target_name': 'browser_ui',
       'type': 'static_library',
       'variables': { 'enable_wexit_time_destructors': 1, },
@@ skipping 2557 matching lines @@
         'browser/ui/webui/signin/inline_login_ui.cc',
         'browser/ui/webui/signin/inline_login_ui.h',
         'browser/ui/webui/signin/login_ui_service.cc',
         'browser/ui/webui/signin/login_ui_service.h',
         'browser/ui/webui/signin/login_ui_service_factory.cc',
         'browser/ui/webui/signin/login_ui_service_factory.h',
         'browser/ui/webui/signin/profile_signin_confirmation_dialog.h',
         'browser/ui/webui/signin/profile_signin_confirmation_dialog.cc',
         'browser/ui/webui/signin/profile_signin_confirmation_ui.h',
         'browser/ui/webui/signin/profile_signin_confirmation_ui.cc',
+        'browser/ui/webui/signin/signin_ui.cc',
+        'browser/ui/webui/signin/signin_ui.h',
         'browser/ui/webui/signin/user_manager_screen_handler.h',
         'browser/ui/webui/signin/user_manager_screen_handler.cc',
         'browser/ui/webui/signin/user_manager_ui.h',
         'browser/ui/webui/signin/user_manager_ui.cc',
         'browser/ui/webui/signin_internals_ui.cc',
         'browser/ui/webui/signin_internals_ui.h',
         'browser/ui/webui/suggestions_internals/suggestions_internals_ui.cc',
         'browser/ui/webui/suggestions_internals/suggestions_internals_ui.h',
         'browser/ui/webui/suggestions_internals/suggestions_internals_ui_handler.cc',
         'browser/ui/webui/suggestions_internals/suggestions_internals_ui_handler.h',
@@ skipping 810 matching lines @@
             'browser/ui/webui/local_discovery/local_discovery_ui.cc',
             'browser/ui/webui/local_discovery/local_discovery_ui.h',
             'browser/ui/webui/local_discovery/local_discovery_ui_handler.cc',
             'browser/ui/webui/local_discovery/local_discovery_ui_handler.h',
           ],
         }],
       ],
     },
   ],
 }