cert_net/ contains certificate functionality that depends on network loading
(OCSP, CRL, AIA fetching).
The implementation in this directory is built on URLRequest. See also
services/cert_verifier/cert_net_url_loader/ for an implementation built on
URLLoader.
Conceptually certificates (net/cert/) is a separable concept from net/ and
may end up becoming its own build target. This file organization encourages not
adding dependencies in cert/ for doing network loading. Instead that code
should be placed here.