Adds QUIC_VERSION_36 which adds support to force HOL blocking between streams for measurement purposes. Protected by --quic_enable_version_36.

Force HOL blocking between streams by tunneling all stream data through the
headers stream encapsulated in HTTP/2.0 data frames.  The experiment
will be triggered via Finch setting a new QUIC config parameter
|force_hol_blocking| (tag FHOL).

This will be the basis for comparison between QUIC and
QUIC+FHOL to separate HOL performance impacts from all the
other QUIC benefits (zero rtt, better loss recovery, etc.).

Merge internal change: 126418608

R=rch@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2115033002
Cr-Commit-Position: refs/heads/master@{#404245}
25 files changed