At a glance through https://developer.chrome.com/apps/sockets_tcp, it appears all we need to is to plumb though the "tls1.3" constant and, of course, flip the default. Otherwise it should hopefully just work.

Context for extensions folks: TLS 1.3 is the new version of TLS. It is backwards-compatible and is safe to enable by default transparently. TLS 1.2 servers will continue to connect just fine, it just means we would speak TLS 1.3 to 1.3-capable servers. Your API appears to be quite minimal and contains nothing that would break when 1.3 is negotiated.