sendMediaInfoMessage_(requestId = 0) {
    const media = {
      'contentId': this.player_.getAssetUri(),
      'streamType': this.player_.isLive() ? 'LIVE' : 'BUFFERED',
      // Sending an empty string for now since it's a mandatory field.
      // We don't have this info, and it doesn't seem to be useful, anyway.
      'contentType': '',
    };
    if (!this.player_.isLive()) {
      // Optional, and only sent when the duration is known.
      media['duration'] = this.video_.duration;
    }
    if (this.metadata_) {
      media['metadata'] = this.metadata_;
    }
    this.sendMediaStatus_(requestId, media);
  }
Composes and sends a mediaStatus message with a mediaInfo component.

@param {number=} requestId
@private