static async computeWastedCSSBytes(artifacts, context) {
    const wastedBytesByUrl = new Map();
    try {
      const unusedCssItems = await UnusedCSS.request({
        Stylesheets: artifacts.Stylesheets,
        CSSUsage: artifacts.CSSUsage,
        devtoolsLog: artifacts.DevtoolsLog,
      }, context);
      for (const item of unusedCssItems) {
        wastedBytesByUrl.set(item.url, item.wastedBytes);
      }
    } catch {}

    return wastedBytesByUrl;
  }
@param {LH.Artifacts} artifacts
@param {LH.Audit.Context} context
@return {Promise<Map<string, number>>}