isBuffered(contentType, time) {
    const ContentType = shaka.util.ManifestParserUtils.ContentType;
    if (contentType == ContentType.TEXT) {
      return this.textEngine_.isBuffered(time);
    } else {
      const buffered = this.getBuffered_(contentType);
      return shaka.media.TimeRangesUtils.isBuffered(buffered, time);
    }
  }
Determines if the given time is inside the buffered range of the given
content type.

@param {shaka.util.ManifestParserUtils.ContentType} contentType
@param {number} time Playhead time
@return {boolean}