When HttpProxyClientSocketWrapper creates a QUIC or H2 stream, it passes in the priority it was created with.  We then return a proxied StreamSocket that has that priority.  Then either SSL is layered on top of the StreamSocket, or an H2 session is.  Either way, the StreamSocket maintains its original priority, while the priority of the highest priority current consumer of the SSL socket or H2 stream changes over time.

It seems like the simplest option is to just always use the same default priority here, though we could look into doing better than that.