Add Util.renderPerformanceCategoryForPSI()

[paulirish]

Expose a single API for PSI to use.

something like:

/** @typedef {import('./dom.js')} DOM */
/** @typedef {import('./psi-renderer.js')} PSIReportRenderer */

/**
 * @param {string} LHresponseJsonString
 * @return {Element}
 */
function renderPerformanceCategoryForPSI(lighthouseResponse) {
  var lighthouseJson = JSON.parse(lighthouseResponse);
  const dom = new DOM(document);

  const reportLHR = JSON.parse(JSON.stringify(lighthouseJson));
  reportLHR.reportCategories = Object.values(reportLHR.categories);
  ReportRenderer.smooshAuditResultsIntoCategories(reportLHR.audits, reportLHR.reportCategories);
  const perfCategory = reportLHR.reportCategories.find(cat => cat.id === 'performance');
  const perfRenderer = new PerformanceCategoryRenderer(dom, new DetailsRenderer(dom));
  const perfEl = perfRenderer.render(perfCategory, reportLHR.categoryGroups);

  const scoreGaugeEl = dom.find('.lh-score__gauge', perfEl);
  const scoreGaugeWrapper = dom.find('.lh-gauge__wrapper', scoreGaugeEl);
  scoreGaugeWrapper.classList.add('lh-gauge__wrapper--huge');
  scoreGaugeWrapper.removeAttribute('href');
  dom.find('.lh-category-header', perfEl).remove();
  dom.find('.lh-permalink', perfEl).remove();

  const datauri = PerformanceCategoryRenderer.getLastScreenshot(perfCategory);

  return [scoreGaugeEl, perfEl, datauri];
};