Add chrome://site-engagement WebUI.

chrome/browser/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//third_party/protobuf/proto_library.gni")
 
@@ skipping 911 matching lines @@
 # GYP version: chrome/chrome_resources.gyp:chrome_resources
 # (generate_browser_resources action)
 grit("resources") {
   source = "browser_resources.grd"
   output_dir = "$root_gen_dir/chrome"
   outputs = [
     "grit/browser_resources.h",
     "browser_resources.pak",
   ]
 
-  omnibox_mojom_file =
-      "$root_gen_dir/chrome/browser/ui/webui/omnibox/omnibox.mojom.js"
-
   grit_flags = [
     "-E",
     "about_credits_file=" + rebase_path(about_credits_file, root_build_dir),
     "-E",
     "additional_modules_list_file=" +
         rebase_path(additional_modules_list_file, root_build_dir),
     "-E",
-    "omnibox_mojom_file=" + rebase_path(omnibox_mojom_file, root_build_dir),
+    "root_gen_dir=" + rebase_path(root_gen_dir, root_build_dir),
   ]
 
   deps = [
     ":about_credits",
     ":chrome_internal_resources_gen",
 
     # Depend only on the generated mojo bindings since we read the .mojom.js
     # file, rather than the whole mojo target which will link the C++ bindings.
+    "//chrome/browser/ui/webui/engagement:mojo_bindings__generator",
     "//chrome/browser/ui/webui/omnibox:mojo_bindings__generator",
   ]
-  inputs = [
-    omnibox_mojom_file,
-  ]
 }
 
 # GYP version: chrome/chrome_resource.gyp:about_credits
 action("about_credits") {
   script = "//tools/licenses.py"
 
   inputs = [
     # This is not a complete list. TODO(phajdan.jr, dbeam): licenses.py needs to
     # generate a .d file with all the licenses/credits that about:credits uses.
     # Then about:credits will automatically rebuild when one of them changes.
@@ skipping 286 matching lines @@
         rebase_path(gypi_values.chrome_browser_rlz_sources, ".", "//chrome")
     deps = [
       "//components/google/core/browser",
       "//components/omnibox/browser",
       "//components/rlz",
       "//components/search_engines",
       "//rlz:rlz_lib",
     ]
   }
 }