GitLab

Using async functions and promise_tests instead of then()-chains and
async_tests. This makes them more readable, easier to maintain and
shorter.

Replaced RTCPeerConnection-helper.js function performOffer() with
exchangeOffer()/exchangeAnswer()/exchangeOfferAnswer().

Updated tests that were performing multiple offers to perform a full
offer/answer exchange whenever there were future offers to be made.
Previously it would perform half of an offer/answer cycle before
starting the next offer/answer, which under Unified Plan could lead to
some unexpected failures.

TBR=guidou@chromium.org

Bug: 777617
Change-Id: Ib0305d55af5aef7f49b5418d4ba44ded9c84d5c6
Reviewed-on: https://chromium-review.googlesource.com/1082434Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565234}