Change QuicStreamRequest::Request() to take a preferred QuicVersion so that
the created QuicConnection will use the designated QuicVersion instead
of hardcoded QuicVersion in HttpNetworkSession::Param().quic_supported_versions.

BUG=689762

Review-Url: https://codereview.chromium.org/2958133002
Cr-Commit-Position: refs/heads/master@{#484769}
12 files changed