bufferedAheadOf(contentType, time) {
    const ContentType = shaka.util.ManifestParserUtils.ContentType;
    if (contentType == ContentType.TEXT) {
      return this.textEngine_.bufferedAheadOf(time);
    } else {
      const buffered = this.getBuffered_(contentType);
      return shaka.media.TimeRangesUtils.bufferedAheadOf(buffered, time);
    }
  }
Computes how far ahead of the given timestamp is buffered for the given
content type.

@param {shaka.util.ManifestParserUtils.ContentType} contentType
@param {number} time
@return {number} The amount of time buffered ahead in seconds.