chromium/chrome/test/data/extensions/platform_apps/web_view/post_message/basic/guest.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.
-->
<script>
window.addEventListener('message', function(e) {
  window.console.log('post message received.');
  var data = JSON.parse(e.data);
  if (data.length == 1 && data[0] === 'ping') {
    e.source.postMessage(JSON.stringify(['pong']), '*');
  }
});
</script>