GitLab

* Remove HttpNetworkSession::enabled_protocols_.
* Spell out AlternateProtocol enum values in
  HttpNetworkSession::IsProtocolEnabled() and in
  HttpServerProperties::IsAlternateProtocolValid().
* Remove ALTERNATE_PROTOCOL_MAXIMUM_VALID_VERSION,
  ALTERNATE_PROTOCOL_MINIMUM_VALID_VERSION, enum AlternateProtocolSize.

BUG=116575

Review-Url: https://codereview.chromium.org/2362233002
Cr-Commit-Position: refs/heads/master@{#420731}