[content shell] add support for dumping frame load callbacks

content/renderer/render_view_impl.cc

Index: content/renderer/render_view_impl.cc
diff --git a/content/renderer/render_view_impl.cc b/content/renderer/render_view_impl.cc
index 37d1011dc930132ba83deb303b2f85c65398c999..07a4ac5c19bcad99893483685020694f39ff49b5 100644
--- a/content/renderer/render_view_impl.cc
+++ b/content/renderer/render_view_impl.cc
@@ -3253,6 +3253,12 @@ void RenderViewImpl::ProcessAcceleratedPinchZoomFlags(
 
 void RenderViewImpl::didStartProvisionalLoad(WebFrame* frame) {
   WebDataSource* ds = frame->provisionalDataSource();
+
+  // In fast/loader/stop-provisional-loads.html, we abort the load before this
+  // callback is invoked.
+  if (!ds)
+    return;
+
   DocumentState* document_state = DocumentState::FromDataSource(ds);
 
   // We should only navigate to swappedout:// when is_swapped_out_ is true.