PlzNavigate: Add metrics to understand bf navigations PLT regression

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 58d198c46d551a4b476b725afff6ae85e64c8d47..eb533214e06b81bead231e90004cab13dd4e018a 100644
--- a/content/browser/frame_host/navigation_handle_impl.h
+++ b/content/browser/frame_host/navigation_handle_impl.h
@@ -486,6 +486,9 @@ class CONTENT_EXPORT NavigationHandleImpl : public NavigationHandle {
   // The time this navigation started.
   const base::TimeTicks navigation_start_;
 
+  // The time this naviagtion was ready to commit.
+  base::TimeTicks ready_to_commit_time_;
+
   // The unique id of the corresponding NavigationEntry.
   int pending_nav_entry_id_;