merge_pr_27

Re-enable testing of wpt/webrtc/RTCPeerConnection-setRemoteDescription-rollback.html and improve some test cases

Bug: chromium:1025557
Change-Id: I5be63e394c830faf55442d62a053e100875de5a0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1932793
Commit-Queue: Eldar Rello elrello@microsoft.com
Commit-Queue: Henrik Boström hbos@chromium.org
Reviewed-by: Henrik Boström hbos@chromium.org
Reviewed-by: Harald Alvestrand hta@chromium.org
Cr-Commit-Position: refs/heads/master@{#719106}