blink::mojom::MimeRegistryProxy::GetMimeTypeFromExtension(mojo::String const &,mojo::String *) is showing up in quite a few renderer hangs for SyncHandleRegistry::WatchAllHandles. This means it's not getting its reply.

Might be a bug in the browser-side implementation, or it might just be a symptom of other hangs in the browser. Needs further investigation.

Assigning to myself until I can triage further.