Add a chrome://interstitials page.

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': {
     'chrome_browser_ui_non_ios_sources': [
       'browser/ui/accelerator_utils.h',
       'browser/ui/android/android_about_app_info.cc',
       'browser/ui/android/android_about_app_info.h',
@@ skipping 1612 matching lines @@
       'browser/ui/webui/help/version_updater.h',
       'browser/ui/webui/help/version_updater_chromeos.cc',
       'browser/ui/webui/help/version_updater_chromeos.h',
       'browser/ui/webui/help/version_updater_mac.h',
       'browser/ui/webui/help/version_updater_mac.mm',
       'browser/ui/webui/help/version_updater_win.cc',
       'browser/ui/webui/identity_internals_ui.cc',
       'browser/ui/webui/identity_internals_ui.h',
       'browser/ui/webui/inspect_ui.cc',
       'browser/ui/webui/inspect_ui.h',
+      'browser/ui/webui/interstitials/interstitial_ui.cc',
+      'browser/ui/webui/interstitials/interstitial_ui.h',
       'browser/ui/webui/ntp/app_launcher_handler.cc',
       'browser/ui/webui/ntp/app_launcher_handler.h',
       'browser/ui/webui/ntp/app_resource_cache_factory.cc',
       'browser/ui/webui/ntp/app_resource_cache_factory.h',
       'browser/ui/webui/ntp/core_app_launcher_handler.cc',
       'browser/ui/webui/ntp/core_app_launcher_handler.h',
       'browser/ui/webui/ntp/favicon_webui_handler.cc',
       'browser/ui/webui/ntp/favicon_webui_handler.h',
       'browser/ui/webui/ntp/foreign_session_handler.cc',
       'browser/ui/webui/ntp/foreign_session_handler.h',
@@ skipping 1278 matching lines @@
         ['enable_webrtc==1', {
           'sources': [ '<@(chrome_browser_ui_webrtc_sources)' ],
         }],
         ['enable_service_discovery==1', {
           'sources': [ '<@(chrome_browser_ui_service_discovery_sources)' ],
         }],
       ],
     },
   ],
 }