[page_load_metrics] Get navigation_start from NavigationHandle

components/page_load_metrics/browser/metrics_web_contents_observer.h

Index: components/page_load_metrics/browser/metrics_web_contents_observer.h
diff --git a/components/page_load_metrics/browser/metrics_web_contents_observer.h b/components/page_load_metrics/browser/metrics_web_contents_observer.h
index bab17808998425f3349d71da3b036b7679091f68..b7326da87f19f46cbe324f46af9507cd836ca673 100644
--- a/components/page_load_metrics/browser/metrics_web_contents_observer.h
+++ b/components/page_load_metrics/browser/metrics_web_contents_observer.h
@@ -184,6 +184,7 @@ class PageLoadTracker {
  public:
   // Caller must guarantee that the observers pointer outlives this class.
   PageLoadTracker(bool in_foreground,
+                  content::NavigationHandle* navigation_handle,
                   rappor::RapporService* const rappor_service,
                   base::ObserverList<PageLoadMetricsObserver, true>* observers);
   ~PageLoadTracker();
@@ -208,6 +209,9 @@ class PageLoadTracker {
 
   bool has_commit_;
 
+  // The navigation start in TimeTicks, not the wall time reported by Blink.
+  const base::TimeTicks navigation_start_;
+
   // We record separate metrics for events that occur after a background,
   // because metrics like layout/paint are delayed artificially
   // when they occur in the background.