chromium/content/test/data/media/webaudio/playback-test.html

<!doctype html>
<html>
  <head>
    <title>Test AudioContextManager Audible Playback</title>
  </head>

  <body>
    <script>
      let context = new AudioContext();
      let osc = new OscillatorNode(context);
      // Set initial gain to 0 to make sure we start with silence.
      let gain = new GainNode(context, {gain: 0});

      // Connect everything and start the oscillator.  The browser test will set the gain value as
      // needed to test if the messages are being sent.
      osc.connect(gain).connect(context.destination);
      osc.start();

    </script>
  </body>
</html>