[CustomTabs] Report the navigation start as absolute time

chrome/browser/page_load_metrics/observers/android_page_load_metrics_observer.h

Index: chrome/browser/page_load_metrics/observers/android_page_load_metrics_observer.h
diff --git a/chrome/browser/page_load_metrics/observers/android_page_load_metrics_observer.h b/chrome/browser/page_load_metrics/observers/android_page_load_metrics_observer.h
index 5916cbfd1ccaf9c6ceda2fe68ac495bff145fb70..ceee273d4ebc0abd22c3ff2ab0945ea2476571cb 100644
--- a/chrome/browser/page_load_metrics/observers/android_page_load_metrics_observer.h
+++ b/chrome/browser/page_load_metrics/observers/android_page_load_metrics_observer.h
@@ -23,12 +23,16 @@ class AndroidPageLoadMetricsObserver
   explicit AndroidPageLoadMetricsObserver(content::WebContents* web_contents);
 
   // page_load_metrics::PageLoadMetricsObserver:
+  ObservePolicy OnStart(content::NavigationHandle* navigation_handle,
+                        const GURL& currently_committed_url,
+                        bool started_in_foreground) override;
   void OnFirstContentfulPaint(
       const page_load_metrics::PageLoadTiming& timing,
       const page_load_metrics::PageLoadExtraInfo& extra_info) override;
 
  private:
   content::WebContents* web_contents_;
+  base::TimeTicks navigation_start_;
 
   DISALLOW_COPY_AND_ASSIGN(AndroidPageLoadMetricsObserver);
 };