C++ unit tests for RTCQuicTransport

This CL adds tests for the RTCQuicTransport Blink bindings against a
mock P2PQuicTransport.

Bug: 874296
Change-Id: I3d41ab19a359948d47e57bbc76fe767a20300ebc
Reviewed-on: https://chromium-review.googlesource.com/c/1260382
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Steve Anton <steveanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598963}
16 files changed