Landing Recent QUIC changes until Thu Apr 20 2017

Convert QUIC non-feature flags to the old syntax, for consistency.

Merge internal change: 153720286

Increases inflight limit for QUIC BBR if the ack rate in the past half-rtt was  lower than half the current bandwidth estimate.

Protected by FLAGS_quic_reloadable_flag_quic_bbr_slow_recent_delivery.

Merge internal change: 153663187

Include unistd.h in

Merge internal change: 153540629

Remain in packet conservation mode if BBR is in PROBE_BW and not in high-gain mode.  Protected by FLAGS_quic_reloadable_flag_quic_bbr_extra_conservation.

Merge internal change: 153506591

Cr-Commit-Position: refs/heads/master@{#466169}
14 files changed