chromium/chrome/test/data/extensions/platform_apps/web_view/autoplay/guest.js

// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

window.addEventListener('message', function() {
  var audio = document.createElement('audio');
  audio.src = 'test.mp4';
  audio.play().then(() => {
    console.log('autoplayed');
  }, e => {
    console.log(e.name);
  });
});