PlzNavigate: fix timing issue in app window creation

content/browser/frame_host/navigator_delegate.h

Index: content/browser/frame_host/navigator_delegate.h
diff --git a/content/browser/frame_host/navigator_delegate.h b/content/browser/frame_host/navigator_delegate.h
index ac8402c9f6e67021004f2b746041e381c6dcac23..14ab69b5733310c42105a3f534ea00dba2bf7680 100644
--- a/content/browser/frame_host/navigator_delegate.h
+++ b/content/browser/frame_host/navigator_delegate.h
@@ -34,6 +34,9 @@ class CONTENT_EXPORT NavigatorDelegate {
   // Called when a navigation was redirected.
   virtual void DidRedirectNavigation(NavigationHandle* navigation_handle) {}
 
+  // Called when the navigation is about to be committed in a renderer.
+  virtual void ReadyToCommitNavigation(NavigationHandle* navigation_handle) {}
+
   // Called when a navigation committed.
   virtual void DidCommitNavigation(NavigationHandle* navigation_handle) {}