static mapSheetToResult(stylesheetInfo) {
    let url = stylesheetInfo.header.sourceURL;
    if (!url || stylesheetInfo.header.isInline) {
      const contentPreview = UnusedCSS.determineContentPreview(stylesheetInfo.content);
      url = contentPreview;
    }

    const usage = UnusedCSS.computeUsage(stylesheetInfo);
    return {url, ...usage};
  }
@param {StyleSheetInfo} stylesheetInfo The stylesheetInfo object.
@return {LH.Audit.ByteEfficiencyItem}