[page_load_metrics] Get navigation_start from NavigationHandle

content/browser/frame_host/navigation_handle_impl.cc

Index: content/browser/frame_host/navigation_handle_impl.cc
diff --git a/content/browser/frame_host/navigation_handle_impl.cc b/content/browser/frame_host/navigation_handle_impl.cc
index 7ffc6b4157b72a85cbbce5a9b95ea788c49a7d81..2976356180b7ac03539a1bece7b8b3d3dd923e46 100644
--- a/content/browser/frame_host/navigation_handle_impl.cc
+++ b/content/browser/frame_host/navigation_handle_impl.cc
@@ -99,6 +99,10 @@ bool NavigationHandleImpl::IsInMainFrame() {
   return frame_tree_node_->IsMainFrame();
 }
 
+const base::TimeTicks& NavigationHandleImpl::navigation_start() {
+  return navigation_start_;
+}
+
 bool NavigationHandleImpl::IsPost() {
   CHECK_NE(INITIAL, state_)
       << "This accessor should not be called before the request is started.";