function requestViaAudio(url) {
  return createMediaElement("audio",
                            {},
                            {"type": "audio/wav", "src": url}).eventPromise;
}
Creates a new audio element, binds loadeddata and error events, sets
    attributes and source URL and appends to {@code document.body}.
@param {string} url The URL of the audio.
@return {Promise} The promise for success/error events.