Create NavigationHandle after beforeunload with PlzNavigate.

content/browser/frame_host/frame_tree_node.cc

Index: content/browser/frame_host/frame_tree_node.cc
diff --git a/content/browser/frame_host/frame_tree_node.cc b/content/browser/frame_host/frame_tree_node.cc
index 0fadcaa8afb6208aa9e8cc06439e864a03a492eb..237f3f9a18a91d7480899f2783cded9a370a3756 100644
--- a/content/browser/frame_host/frame_tree_node.cc
+++ b/content/browser/frame_host/frame_tree_node.cc
@@ -400,7 +400,7 @@ void FrameTreeNode::CreatedNavigationRequest(
   // RenderFrameHostManager will take care of updates to the speculative
   // RenderFrameHost in DidCreateNavigationRequest below.
   if (was_previously_loading) {
-    if (navigation_request_) {
+    if (navigation_request_ && navigation_request_->navigation_handle()) {
       // Mark the old request as aborted.
       navigation_request_->navigation_handle()->set_net_error_code(
           net::ERR_ABORTED);
@@ -503,10 +503,14 @@ void FrameTreeNode::DidChangeLoadProgress(double load_progress) {
 bool FrameTreeNode::StopLoading() {
   if (IsBrowserSideNavigationEnabled()) {
     if (navigation_request_) {
-      navigation_request_->navigation_handle()->set_net_error_code(
-          net::ERR_ABORTED);
-      navigator_->DiscardPendingEntryIfNeeded(
-          navigation_request_->navigation_handle());
+      int expected_pending_nav_entry_id = navigation_request_->nav_entry_id();
+      if (navigation_request_->navigation_handle()) {
+        navigation_request_->navigation_handle()->set_net_error_code(
+            net::ERR_ABORTED);
+        expected_pending_nav_entry_id =
+            navigation_request_->navigation_handle()->pending_nav_entry_id();
+      }
+      navigator_->DiscardPendingEntryIfNeeded(expected_pending_nav_entry_id);
     }
     ResetNavigationRequest(false, true);
   }
@@ -541,6 +545,11 @@ void FrameTreeNode::BeforeUnloadCanceled() {
         render_manager_.speculative_frame_host();
     if (speculative_frame_host)
       speculative_frame_host->ResetLoadingState();
+    // Note: there is no need to set an error code on the NavigationHandle here
+    // as it has not been created yet. It is only created when the
+    // BeforeUnloadACK is received.
+    if (navigation_request_)
+      ResetNavigationRequest(false, true);
   } else {
     RenderFrameHostImpl* pending_frame_host =
         render_manager_.pending_frame_host();