Currently we have net/socket/ssl_client_socket.h and net/socket/ssl_client_socket_impl.h.

SSLClientSocket has three public static methods:
- SetSSLKeyLogFile
- IgnoreCertError
- ClearSessionCache

SSLClientSocket has one protected static method:
- SerializeNextProtos

It also has two private members:
- signed_cert_timestamps_received_
- stapled_ocsp_response_received_

The protected/private members are only used by test (and the latter two can be tested using CTVerifier/CertVerifier interfaces, thus don't need to exist as they do), while the former three public methods all just delegate to the Impl

We should clean this up and unify these classes so we don't have an unnecessary and arbitrary split.

Further, two of the public static methods - ClearSessionCache and SetSSLKeyLogFile - are logically part of the SSLClientSocketContext, as noted in the header.