Allow number of open QUIC streams to grow 10% beyond configured limit at

Allow number of open QUIC streams to grow 10% beyond configured limit at
the QUIC internal server before closing connection.

In the following situation Chrome may open more streams than the
configured limit:

* opens kMaxStreams streams
* sends a FIN for one of the streams, now has kMaxStreams-1 streams open
* opens a new stream
* FIN gets lost on way to QUIC internal server
* QUIC internal server terminates connection when new stream packet
  arrives

Rather than making Chrome keep track of when the server has acknowledged
a FIN, just give 10% breathing room which should avoid this case.

Merge internal change: 75393293

R=rch@chromium.org, rjshade@chromium.org

[Ryan Hamilton, 2014-09-15 21:43:52]

lgtm