Only close the QUIC connection after 5RTOs on the client side when the

Only close the QUIC connection after 5RTOs on the client side when the
5RTO connection option is present. Protected by ENABLED
FLAGS_quic_only_5rto_client_side.

For users with relatively short RTTs, the 5th RTO on the server side can
occur before the client sends a PING.  In networks with short NAT
timeouts, this causes the connection to be abruptly closed once the NAT
tunnel is re-opened by the client's PING, instead of receiving the
response.

Merge internal change: 133030062

R=ianswett@chromium.org, rch@chromium.org
BUG=

[Jana, 2016-09-19 19:19:31]

The CQ bit was checked by jri@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-09-19 19:20:04]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Ryan Hamilton, 2016-09-19 19:33:16]

lgtm

[commit-bot: I haz the power, 2016-09-19 20:25:12]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-09-19 20:25:13]

Dry run: This issue passed the CQ dry run.