Add chrome://site-engagement WebUI.

chrome/chrome_resources.gyp

 # 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': {
     'grit_out_dir': '<(SHARED_INTERMEDIATE_DIR)/chrome',
     'about_credits_file': '<(SHARED_INTERMEDIATE_DIR)/about_credits.html',
     'additional_modules_list_file': '<(SHARED_INTERMEDIATE_DIR)/chrome/browser/internal/additional_modules_list.txt',
-    'omnibox_mojom_file': '<(SHARED_INTERMEDIATE_DIR)/chrome/browser/ui/webui/omnibox/omnibox.mojom.js',
   },
   'targets': [
     {
       # GN version: //chrome:extra_resources
       'target_name': 'chrome_extra_resources',
       'type': 'none',
       # These resources end up in resources.pak because they are resources
       # used by internal pages.  Putting them in a separate pak file makes
       # it easier for us to reference them internally.
       'actions': [
@@ skipping 167 matching lines @@
       ],
       'actions': [
         {
           # GN version: //chrome/browser:resources
           'action_name': 'generate_browser_resources',
           'variables': {
             'grit_grd_file': 'browser/browser_resources.grd',
             'grit_additional_defines': [
               '-E', 'about_credits_file=<(about_credits_file)',
               '-E', 'additional_modules_list_file=<(additional_modules_list_file)',
-              '-E', 'omnibox_mojom_file=<(omnibox_mojom_file)',
+              '-E', 'root_gen_dir=<(SHARED_INTERMEDIATE_DIR)',
             ],
           },
           'includes': [ '../build/grit_action.gypi' ],
         },
         {
           # GN version: //chrome/common:resources
           'action_name': 'generate_common_resources',
           'variables': {
             'grit_grd_file': 'common/common_resources.grd',
           },
@@ skipping 449 matching lines @@
                      '<(generator_path)',
                      'credits',
                      '<(about_credits_file)',
           ],
           'message': 'Generating about:credits',
         },
       ],
     },
   ], # targets
 }