Updates to P2PQuicTransport tests.

As part of the effort to add read/write to the P2PQuicTransportStream,
some of the stream level tests need to be moved into their own more
isolated testing environment. This includes using a MockQuicSession.
This change moves the stream unit tests to this new environment, and
also updates the p2p_quic_transport_test.cc to use Mock objects instead
of the fake objects for the delegates.

Bug: 874296
Change-Id: Ifdfd30f753a2b6090c8f73330978c5feed2b9cf6
Reviewed-on: https://chromium-review.googlesource.com/c/1312971
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Seth Hampson <shampson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605753}
7 files changed