combineBaselineAndComputedDatasets(siteIndexWithComputed, baselineLanternData) {
    for (const site of baselineLanternData.sites) {
      const computedSite = siteIndexWithComputed.sites.find(entry => entry.url === site.url);
      if (!computedSite) continue;
      computedSite.baseline = site;
    }

    const entries = siteIndexWithComputed.sites.filter(site => site.lantern && site.baseline);

    if (!entries.length) {
      throw new Error('No lantern metrics available, did you run run-on-all-assets.js?');
    }

    return entries;
  }
@param {{sites: Array<LanternSiteDefinition>}} siteIndexWithComputed
@param {{sites: Array<LanternMetrics & {url: string}>}} baselineLanternData