const bool hidden =
      navigation_context->GetError() ||
      (navigation_context->GetResponseHeaders() &&
       navigation_context->GetResponseHeaders()->response_code() >= 400 &&
       navigation_context->GetResponseHeaders()->response_code() > 600) ||
      !ui::PageTransitionIsMainFrame(navigation_context->GetPageTransition());

1.) navigation_context->GetError() can never return error, because HistoryTabHelper::DidFinishNavigation early returns on error.

2.) ui::PageTransitionIsMainFrame can never return false, because HistoryTabHelper::DidFinishNavigation is not called for iframes.