Adding an end-to-end connection time test.

The test uses a fake clock and simulates network and signaling delays in
order to get a repeatable measurement of the time to establish a
connection (including DTLS). This will help ensure that various
optimizations continue to work as expected, and no new delays are
introduced.

This CL depends on: https://codereview.webrtc.org/2140283002/

R=honghaiz@webrtc.org, pthatcher@webrtc.org, skvlad@webrtc.org

Review URL: https://codereview.webrtc.org/2141863003 .

Cr-Commit-Position: refs/heads/master@{#14270}