* move CHECK statements into DEBUG checks
* improve performance by removing branches
* Several if checks were left in while the code was being developed.
Now that the core API has stablized more, the checks are largely
unnecessary and can be removed, yielding a significant boost in
performance.
* refactor flow control for proper backpressure
* use std::queue for inbound headers
* use std::queue for outbound data
* remove now unnecessary FreeHeaders function
* expand comments and miscellaneous edits
* add a couple of misbehaving flow control tests
PR-URL: https://github.com/nodejs/node/pull/16239
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
