[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 3cc08830636be60471e40c7f140d8f31eb3c2d0a..f0a6bc02730e6897e571a3fe4080cd29aaf7e595 100644
--- a/components/page_load_metrics/browser/metrics_web_contents_observer.h
+++ b/components/page_load_metrics/browser/metrics_web_contents_observer.h
@@ -195,6 +195,7 @@ class PageLoadTracker {
   // outlives this class.
   PageLoadTracker(bool in_foreground,
                   PageLoadMetricsEmbedderInterface* embedder_interface,
+                  content::NavigationHandle* navigation_handle,
                   base::ObserverList<PageLoadMetricsObserver, true>* observers);
   ~PageLoadTracker();
   void Commit(content::NavigationHandle* navigation_handle);
@@ -218,6 +219,9 @@ 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.