Add expected_connection_id_length to QuicFramer

This CL introduces the variable expected_connection_id_length to
QuicFramer, which represents how many bytes of connection ID a streamer
should read when parsing incoming short IETF headers. In order for this
to be configured by quartc and by our test code, it needed to be plumbed
through the QuicDispatcher and QuicServer as well.

Merge internal change: 237337808

R=rch@chromium.org

Change-Id: I90393552e1269fb142f6154ba639d63af8bd62d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1510295
Reviewed-by: Ryan Hamilton <rch@chromium.org>
Commit-Queue: Ryan Hamilton <rch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638913}
34 files changed