async loadFromGistUrl(urlStr) {
    try {
      const url = new URL(urlStr);

      if (url.origin !== 'https://gist.github.com') {
        logger.error('URL was not a gist');
        return;
      }

      const match = url.pathname.match(/[a-f0-9]{5,}/);
      if (match) {
        const gistId = match[0];
        history.pushState({}, '', `${LighthouseTreemap.APP_URL}?gist=${gistId}`);
        const json = await this._github.getGistFileContentAsJson(gistId);
        const options = this.coerceToOptions(json);
        this.init(options);
      }
    } catch (err) {
      logger.error(err);
    }
  }
Loads report json from gist URL, if valid. Updates page URL with gist id
and loads from GitHub.
@param {string} urlStr gist URL