[WebUI] Add a chrome://prefs-internals page

chrome/test/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/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//chrome/common/features.gni")
@@ skipping 1822 matching lines @@
       "../browser/ui/webui/options/content_settings_exception_area_browsertest.cc",
       "../browser/ui/webui/options/multilanguage_options_browsertest.cc",
       "../browser/ui/webui/options/multilanguage_options_browsertest.h",
       "../browser/ui/webui/options/options_browsertest.cc",
       "../browser/ui/webui/options/options_ui_browsertest.cc",
       "../browser/ui/webui/options/options_ui_browsertest.h",
       "../browser/ui/webui/options/preferences_browsertest.cc",
       "../browser/ui/webui/options/preferences_browsertest.h",
       "../browser/ui/webui/password_manager_internals/password_manager_internals_ui_browsertest.cc",
       "../browser/ui/webui/policy_ui_browsertest.cc",
+      "../browser/ui/webui/prefs_internals_browsertest.cc",
       "../browser/ui/webui/print_preview/print_preview_ui_browsertest.cc",
       "../browser/ui/webui/set_as_default_browser_ui_browsertest_win.cc",
       "../browser/ui/webui/settings/md_settings_ui_browsertest.cc",
       "../browser/ui/webui/signin/inline_login_ui_browsertest.cc",
       "../browser/ui/webui/signin/user_manager_ui_browsertest.cc",
       "../browser/ui/webui/task_scheduler_internals/task_scheduler_internals_ui_browsertest.cc",
       "../browser/ui/webui/uber/uber_ui_browsertest.cc",
       "../browser/ui/webui/webui_browsertest.cc",
       "../browser/ui/webui/webui_webview_browsertest.cc",
       "../browser/ui/zoom/zoom_controller_browsertest.cc",
@@ skipping 3334 matching lines @@
 }
 
 if (is_win) {
   loadable_module("conflicts_dll") {
     testonly = true
     sources = [
       "conflicts/conflicts_dll.cc",
     ]
   }
 }