static parseTime_(element, rateInfo) {
    const start = shaka.text.TtmlTextParser.parseTimeAttribute_(
        element.attributes['begin'], rateInfo);
    let end = shaka.text.TtmlTextParser.parseTimeAttribute_(
        element.attributes['end'], rateInfo);
    const duration = shaka.text.TtmlTextParser.parseTimeAttribute_(
        element.attributes['dur'], rateInfo);
    if (end == null && duration != null) {
      end = start + duration;
    }
    return {start, end};
  }
Parse TTML time attributes from the given element.

@param {!shaka.extern.xml.Node} element
@param {!shaka.text.TtmlTextParser.RateInfo_} rateInfo
@return {{start: ?number, end: ?number}}
@private