flush_(contentType) {
    // Never use flush_ if there's data.  It causes a hiccup in playback.
    goog.asserts.assert(
        this.video_.buffered.length == 0, 'MediaSourceEngine.flush_ should ' +
        'only be used after clearing all data!');

    // Seeking forces the pipeline to be flushed.
    this.video_.currentTime -= 0.001;

    // Fake an 'updateend' event to resolve the operation.
    this.onUpdateEnd_(contentType);
  }
Nudge the playhead to force the media pipeline to be flushed.
This seems to be necessary on Chromecast to get new content to replace old
content.
@param {shaka.util.ManifestParserUtils.ContentType} contentType
@private