This stats dictionary is partially supported (see landed CLs in this thread).
To better track what's left, a webrtc bug has been created to track the remaining work related to this dictionary - merging into that one.
This is split up into two bugs, one for the RTCInboundRTPStreamStats case (https://bugs.chromium.org/p/webrtc/issues/detail?id=7065) and one for the RTCOutboundRTPStreamStats case (https://bugs.chromium.org/p/webrtc/issues/detail?id=7066).
Comment 1 by hbos@chromium.org
, Oct 20 2016