Refactor SSLClientSocket::SerializeNextProtos().

Break out HTTP/2 protocol removal from SSLClientSocket::SerializeNextProtos() to
SSLClientSocket::DisableHTTP2() method.  DisableHTTP2() will be used for NPN to
create a NextProtoVector that can be used by the callback function (no
serialization is necessary for this.)

BUG=527066

Review URL: https://codereview.chromium.org/1371263002

Cr-Commit-Position: refs/heads/master@{#351210}
7 files changed