unsigned long long PerformanceTiming::domainLookupStart() const { ResourceLoadTiming* timing = resourceLoadTiming(); if (!timing) return fetchStart(); // This will be zero when a DNS request is not performed. Rather than // exposing a special value that indicates no DNS, we "backfill" with // fetchStart. double dnsStart = timing->dnsStart(); if (dnsStart == 0.0) return fetchStart(); return monotonicTimeToIntegerMilliseconds(dnsStart); }