_renderReportWarnings(report) {
    if (!report.runWarnings || report.runWarnings.length === 0) {
      return this._dom.createElement('div');
    }

    const container = this._dom.createComponent('warningsToplevel');
    const message = this._dom.find('.lh-warnings__msg', container);
    message.textContent = Globals.strings.toplevelWarningsMessage;

    const warnings = [];
    for (const warningString of report.runWarnings) {
      const warning = this._dom.createElement('li');
      warning.append(this._dom.convertMarkdownLinkSnippets(warningString));
      warnings.push(warning);
    }
    this._dom.find('ul', container).append(...warnings);

    return container;
  }
Returns a div with a list of top-level warnings, or an empty div if no warnings.
@param {LH.ReportResult} report
@return {Node}