Spec: https://w3c.github.io/webrtc-stats/#dom-rtcoutboundrtpstreamstats-qualitylimitationdurations Tested in chromium using wpt/webrtc-stats. Bug: webrtc:10686 Change-Id: I05ac344e6caa7a663675de4c06ccfd17e1efb6ee Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/219300 Reviewed-by: Henrik Boström <hbos@webrtc.org> Commit-Queue: Henrik Boström <hbos@webrtc.org> Cr-Commit-Position: refs/heads/master@{#34179}