Update PageLoadTiming to use base::Optional

chrome/browser/page_load_metrics/observers/aborts_page_load_metrics_observer.cc

Index: chrome/browser/page_load_metrics/observers/aborts_page_load_metrics_observer.cc
diff --git a/chrome/browser/page_load_metrics/observers/aborts_page_load_metrics_observer.cc b/chrome/browser/page_load_metrics/observers/aborts_page_load_metrics_observer.cc
index 562c655ed67c2f64afcdb6d62c804ce94fcc868d..e311b7184b7671d20fc8f5a90bac1a7ec9164432 100644
--- a/chrome/browser/page_load_metrics/observers/aborts_page_load_metrics_observer.cc
+++ b/chrome/browser/page_load_metrics/observers/aborts_page_load_metrics_observer.cc
@@ -201,11 +201,11 @@ void AbortsPageLoadMetricsObserver::OnComplete(
   if (timing.IsEmpty())
     return;
 
-  if (!timing.parse_start.is_zero() && time_to_abort >= timing.parse_start &&
-      (timing.parse_stop.is_zero() || timing.parse_stop >= time_to_abort)) {
+  if (timing.parse_start && time_to_abort >= timing.parse_start &&
+      (!timing.parse_stop || timing.parse_stop >= time_to_abort)) {
     RecordAbortDuringParse(abort_type, time_to_abort);
   }
-  if (timing.first_paint.is_zero() || timing.first_paint >= time_to_abort) {
+  if (!timing.first_paint || timing.first_paint >= time_to_abort) {
     RecordAbortAfterCommitBeforePaint(abort_type, time_to_abort);
   }
 }