Heads-up, Chrome 111 introducing "incremental" priorities

[Patrick Meenan <[e-mail]>]

Chrome 111 (currently in dev channel) will be using the incremental flag
for most requests (most everything except for scripts and stylesheets).

Safari already makes use of it but both Firefox and Safari use headers
while Chrome currently uses priority update frames.

IMPORTANT: one big difference is that Chrome currently omits the urgency in
the value of the priority field dictionary if the urgency is the default
and will send an "i" by itself (Safari appears to always send the urgency
explicitly).

I mention this because we're seeing an increase in protocol errors being
reported that coincides with the revision where the flag was added.

So far it looks like the mvfast implementation might not like the priority
string (which appears to be a valid use of the dictionary structured type
but maybe hasn't been exercised) but there may be other implementations
that I'm not aware of that also choke on it (both the Google and Cloudflare
quiche implementations seem to be ok with it).

Thanks,

-Pat