Update tests that broke due to upstream changes of Resolver.

Caused by import:
https://chromium-review.googlesource.com/c/chromium/src/+/1394189

Fixes:
- RTCPeerConnection-remote-track-mute.https.html
- RTCPeerConnection-track-stats.https.html
- RTCPeerConnection-setRemoteDescription-tracks.https.html

The remote-track-mute case was already timing out but would have hit
a problem but it was there for implementations that gets further.

The track-stats problem was in a helper method, it simply caused the
helper to not await for the last step, leading to flaky tests using that
helper.

The SRD-tracks problem had caused Failure instead of Pass, updated the
-expected.txt file and fixed the test.

TBR=hta@chromium.org

Bug: 918768, 919035
Change-Id: I02b855ef411ac1fd7c74d96c8c52aab6fe738201
Reviewed-on: https://chromium-review.googlesource.com/c/1396140
Commit-Queue: Henrik Boström <hbos@chromium.org>
Reviewed-by: Harald Alvestrand <hta@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619911}
5 files changed