Testing at r522488, load a PDF off the disk and press ctrl + F5 to reload. Oftentimes this message comes up:

[148130:148130:1208/171341.711260:ERROR:frame_sink_provider_impl.cc(34)] No RenderWidgetHost exists with id 5 in process 8

We discussed this on https://chromium-review.googlesource.com/c/chromium/src/+/804680 and concluded it is nothing serious. However, it is a bit spammy, and we should try to figure out why it's happening. Ideally reloading a PDF shouldn't log any messages at the default logging level.