Land Recent QUIC Changes.

QUIC - fixing lint errors found while sync'ing with server.

Merge internal change: 56944792

Fix a QUIC bug where the congestion manager was telling the send
algorithm of a loss once one nack was received, but only retransmitted
when 3 were received.

Merge internal change: 56922588

Enables pacing of QUIC packets, via a new flag.  If set, the client
will always use pacing, however, the server will only pace if the
client negotiates pacing.  This allows us to use finch to control the
behavior so we can analyze the performance impact.

Adds a new FLAGS_use_quic_pacing to enable pacing of QUIC packets.
It defaults to false.

Merge internal change: 56869575

Move QUIC's rto count from the connection to the congestion manager.

Merge internal change: 56787945

Use the packet size of CHLO packets to set the QUIC max_packet_size for
the server.

Merge internal change: 56758103

Move QUIC's nack counter into QuicCongestionManager from
QuicSentPacketManager.

Merge internal change: 56746459

Only retransmit the minimum number of packets in QUIC(in TCP's case, 2)
when the RTO fires, instead of retransmitting the entire window.

Based on conversations with Jana, it appears we should be reducing our
congestion window, and the most important mitigation may be implementing
a tail loss probe.

Merge internal change: 56693737

QUIC - minor cleanup of code (lint errors), found while merging.

R=rch@chromium.org

Review URL: https://codereview.chromium.org/77613002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236311 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236311