Issue AboutToNavigateRenderFrame notification after beforeunload handling.

content/browser/frame_host/navigator_impl.cc

Index: content/browser/frame_host/navigator_impl.cc
diff --git a/content/browser/frame_host/navigator_impl.cc b/content/browser/frame_host/navigator_impl.cc
index 53417fc3adacec03cb632be18610979ae65f0956..786fcc7ba1a259d4b15c01987fea56b38f52af30 100644
--- a/content/browser/frame_host/navigator_impl.cc
+++ b/content/browser/frame_host/navigator_impl.cc
@@ -314,7 +314,7 @@ bool NavigatorImpl::NavigateToEntry(
   CheckWebUIRendererDoesNotDisplayNormalURL(dest_render_frame_host, dest_url);
 
   // Notify observers that we will navigate in this RenderFrame.
-  if (delegate_) {
+  if (delegate_ && !dest_render_frame_host->are_navigations_suspended()) {
     delegate_->AboutToNavigateRenderFrame(frame_tree_node->current_frame_host(),

[Charlie Reis, 2015/09/22 23:12:10]

What's happening in AboutToNavigateRenderFrame that must be delayed until after
the beforeunload handler?

I'm confused, because even after this change, the browser process will time out
and allow the navigation to proceed if there's a breakpoint in beforeunload. 
What's different about firing AboutToNavigateRenderFrame later?

[dgozman, 2015/09/22 23:27:55]

It's called from another place.
I didn't know about the timeout. How long is that? I didn't notice it while
testing locally.

[Charlie Reis, 2015/09/22 23:56:42]

That didn't really answer my question, though.

What is DevTools doing in AboutToNavigateRenderFrame that needs to be delayed?
RenderFrameHostImpl::DispatchBeforeUnload sets a timer for kUnloadTimeoutMS,
which is only 1 second.

That means that the navigation will likely try to proceed while the breakpoint
is hit, which seems wrong-- we'll be calling AboutToNavigateRenderFrame 1 second
later than before, but still during the breakpoint.  (I imagine the timeout is
part of the problem in today's behavior as well, though I'm not sure how that
leads to the hang.)

                                           dest_render_frame_host);
   }