Introduce NavigationSimulator to use in unit tests

content/browser/frame_host/render_frame_host_impl.cc

Index: content/browser/frame_host/render_frame_host_impl.cc
diff --git a/content/browser/frame_host/render_frame_host_impl.cc b/content/browser/frame_host/render_frame_host_impl.cc
index f74e19a27a75a49ba84ac89963f48479fae5a23b..7a3823c49e83c7684be0791f13780e12cae42810 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -2474,8 +2474,10 @@ void RenderFrameHostImpl::Navigate(
   //
   // Blink doesn't send throb notifications for JavaScript URLs, so it is not
   // done here either.
-  if (!common_params.url.SchemeIs(url::kJavaScriptScheme))
+  if (!common_params.url.SchemeIs(url::kJavaScriptScheme) &&
+      (!navigation_handle_ || !navigation_handle_->is_transferring())) {
     OnDidStartLoading(true);
+  }
 }
 
 void RenderFrameHostImpl::NavigateToInterstitialURL(const GURL& data_url) {