chromium/chrome/test/data/extensions/platform_apps/web_view/focus_visibility/guest.html

<!DOCTYPE html>
<!--
Copyright 2015 The Chromium Authors
Use of this source code is governed by a BSD-style license that can be
found in the LICENSE file.
-->
<html>
  <body>
    <button> Webview Button </button>
    <script src="./guest.js"></script>
  </body>
</html>