Is your feature request related to a problem? Please describe.

Latest node.js can be compiled with --experimental-http-parser flag. Eventually, we'd want to swap things around and make it enable llhttp parser by default and hide http_parser under --legacy-http-parser flag.

Describe the solution you'd like

Hide http_parser under the flag when we're ready.

Describe alternatives you've considered

No alternatives.

Let's discuss the earliest version of Node that we're going to try this in. http_parser is a major component and it would take a lot of testing to make sure that llhttp is on the par with it quality-wise.

cc @nodejs/release @nodejs/lts