PlzNavigate: don't discard pending entry in DidFailProvisionalLoad

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 9c7c76531f39dbe8068e2a383acebdbcd930d5df..5693e5a36575f3eb5e0f3f1192bb7ab820def609 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -900,6 +900,17 @@ void RenderFrameHostImpl::OnDidFailProvisionalLoadWithError(
   if (!IsBrowserSideNavigationEnabled() && navigation_handle_) {
     navigation_handle_->set_net_error_code(
         static_cast<net::Error>(params.error_code));
+  } else {
+    // The renderer should not be sending this message unless asked to commit
+    // an error page.
+    // TODO(clamy): Stop sending DidFailProvisionalLoad IPCs at all when enough
+    // observers have moved to DidFinishNavigation.
+    if (!navigation_handle_ ||
+        navigation_handle_->GetNetErrorCode() == net::OK) {
+      bad_message::ReceivedBadMessage(
+          GetProcess(), bad_message::RFH_UNEXPECTED_FAIL_PROVISIONAL_LOAD);

[Charlie Reis, 2016/04/11 21:10:57]

The conditions surrounding this will make it hard to diagnose if we see it fail
in practice.  We'll get reports if (1) there's no handle (whether we're in
PlzNavigate or not) or (2) we're in PlzNavigate and the handle says net::OK. 
Those would be very different problems, so maybe we should have separate codes
for them.

That would also let us restructure this method to make it easier to read. 
Something like:

if (!navigation_handle_) {
  ReceivedBadMessage(RFH_FAIL_PROVISIONAL_LOAD_NO_HANDLE)
  return;
}

if (PlzNavigate && net::OK) {
  ReceivedBadMessage(RFH_FAIL_PROVISIONAL_LOAD_NO_ERROR)
  return;
}

if (!PlzNavigate)
  set_net_error_code...
...DidFailProvisionalLoadWithError...

[clamy, 2016/04/12 14:08:01]

Done. It was actually hard enough to read that I though it would only trigger
when PlzNavigate was enabled.

+      return;
+    }
   }
   frame_tree_node_->navigator()->DidFailProvisionalLoadWithError(this, params);
 }