injectFinalScreenshot(categoriesEl, audits, scoreScaleEl) {
    const audit = audits['final-screenshot'];
    if (!audit || audit.scoreDisplayMode === 'error') return null;
    if (!audit.details || audit.details.type !== 'screenshot') return null;

    const imgEl = this.dom.createElement('img', 'lh-final-ss-image');
    const finalScreenshotDataUri = audit.details.data;
    imgEl.src = finalScreenshotDataUri;
    imgEl.alt = audit.title;

    const firstCatHeaderEl = this.dom.find('.lh-category .lh-category-header', categoriesEl);
    const leftColEl = this.dom.createElement('div', 'lh-category-headercol');
    const separatorEl = this.dom.createElement('div',
        'lh-category-headercol lh-category-headercol--separator');
    const rightColEl = this.dom.createElement('div', 'lh-category-headercol');

    leftColEl.append(...firstCatHeaderEl.childNodes);
    leftColEl.append(scoreScaleEl);
    rightColEl.append(imgEl);
    firstCatHeaderEl.append(leftColEl, separatorEl, rightColEl);
    firstCatHeaderEl.classList.add('lh-category-header__finalscreenshot');
  }
Inject the final screenshot next to the score gauge of the first category (likely Performance)
@param {HTMLElement} categoriesEl
@param {LH.ReportResult['audits']} audits
@param {Element} scoreScaleEl