function requestViaPicture(url) {
  var picture = createMediaElement("picture", {}, {"srcset": url,
                                                "type": "image/png"});
  return createRequestViaElement("img", {"src": url}, picture);
}
Creates a new picture element, binds loadeddata and error events, sets
    attributes and source URL and appends to {@code document.body}. Also
    creates new image element appending it to the picture
@param {string} url The URL of the image for the source and image elements.
@return {Promise} The promise for success/error events.