RTCMediaStreamTrackStats.ssrcIds collected by RTCStatsCollector.

webrtc/api/rtcstatscollector.h

Index: webrtc/api/rtcstatscollector.h
diff --git a/webrtc/api/rtcstatscollector.h b/webrtc/api/rtcstatscollector.h
index 4268a215c5f9ae65de50a228711f4887612508d3..34332ed2dae25035a90251674f0b72275d18357e 100644
--- a/webrtc/api/rtcstatscollector.h
+++ b/webrtc/api/rtcstatscollector.h
@@ -156,11 +156,12 @@ class RTCStatsCollector : public virtual rtc::RefCountInterface,
   rtc::scoped_refptr<RTCStatsReport> partial_report_;
   std::vector<rtc::scoped_refptr<RTCStatsCollectorCallback>> callbacks_;
 
-  // Set in |GetStatsReport|, used in |ProducePartialResultsOnNetworkThread|
+  // Set in |GetStatsReport|, read in |ProducePartialResultsOnNetworkThread|
   // (not passed as arguments to avoid copies). This is thread safe - it is set
   // at the start of |GetStatsReport| after making sure there are no pending
   // stats requests in progress.
   std::unique_ptr<ChannelNamePairs> channel_name_pairs_;
+  // ... Also read in |ProducePartialResultsOnSignalingThread|.
   std::unique_ptr<MediaInfo> media_info_;
 
   // A timestamp, in microseconds, that is based on a timer that is