[page_load_metrics] Get navigation_start from NavigationHandle

content/browser/frame_host/navigation_handle_impl.h

Index: content/browser/frame_host/navigation_handle_impl.h
diff --git a/content/browser/frame_host/navigation_handle_impl.h b/content/browser/frame_host/navigation_handle_impl.h
index b0a7b9a36008a11a40eeaca47a28970b330fa8a9..004cf8220eea4fb0252873df2a8749881de87cea 100644
--- a/content/browser/frame_host/navigation_handle_impl.h
+++ b/content/browser/frame_host/navigation_handle_impl.h
@@ -70,6 +70,7 @@ class CONTENT_EXPORT NavigationHandleImpl : public NavigationHandle {
   // NavigationHandle implementation:
   const GURL& GetURL() override;
   bool IsInMainFrame() override;
+  const base::TimeTicks& NavigationStart() override;
   bool IsPost() override;
   const Referrer& GetReferrer() override;
   bool HasUserGesture() override;
@@ -95,11 +96,6 @@ class CONTENT_EXPORT NavigationHandleImpl : public NavigationHandle {
       const GURL& new_referrer_url,
       bool new_is_external_protocol) override;
 
-  // The time the navigation started, recorded either in the renderer or browser
-  // process. Corresponds to Navigation Timing API.
-  // TODO(csharrison): Add this to the public class and mark this override.
-  const base::TimeTicks& navigation_start() { return navigation_start_; }
-
   NavigatorDelegate* GetDelegate() const;
 
   void set_net_error_code(net::Error net_error_code) {