close(id, actual) {
    if (!this.pending_.has(id)) {
      return;
    }

    const estimate = this.pending_.get(id);
    this.pending_.delete(id);

    this.estimatedDownloaded_ += estimate;
    this.actualDownloaded_ += actual;
  }
Close a download in the estimator. This will signal that we have finished
downloading a segment and we can update the progress estimate.

@param {number} id
@param {number} actual