Trace stats in RTCStatsCollector.

webrtc/pc/rtcstatscollector.cc

Index: webrtc/pc/rtcstatscollector.cc
diff --git a/webrtc/pc/rtcstatscollector.cc b/webrtc/pc/rtcstatscollector.cc
index f5b8c8a936c1b569826ff20d98741e62ddb5e550..77ef7c21237671d593b16b998365f45aa585efb4 100644
--- a/webrtc/pc/rtcstatscollector.cc
+++ b/webrtc/pc/rtcstatscollector.cc
@@ -25,6 +25,7 @@
 #include "webrtc/pc/webrtcsession.h"
 #include "webrtc/rtc_base/checks.h"
 #include "webrtc/rtc_base/timeutils.h"
+#include "webrtc/rtc_base/trace_event.h"
 
 namespace webrtc {
 
@@ -431,6 +432,15 @@ ProduceMediaStreamTrackStatsFromVideoSenderInfo(
   // TODO(hbos): Will reduce this by frames dropped due to congestion control
   // when available. crbug.com/659137
   video_track_stats->frames_sent = video_sender_info.frames_encoded;
+  TRACE_EVENT2("webrtc_stats", "sent_frame_width",

[tommi, 2017/07/10 20:43:23]

It would be good to add some context for why these are being traced here and how
it can/should be used. Same below (you could refer to a comment here from the
other places)

+               "value", video_track_stats->frame_width.ValueToString(),
+               "ssrc", video_sender_info.ssrc());
+  TRACE_EVENT2("webrtc_stats", "sent_frame_height",
+               "value", video_track_stats->frame_height.ValueToString(),
+               "ssrc", video_sender_info.ssrc());
+  TRACE_EVENT2("webrtc_stats", "frames_sent",
+               "value", video_track_stats->frames_sent.ValueToString(),
+               "ssrc", video_sender_info.ssrc());
   return video_track_stats;
 }
 
@@ -456,6 +466,12 @@ ProduceMediaStreamTrackStatsFromVideoReceiverInfo(
         video_receiver_info.frame_width);
     video_track_stats->frame_height = static_cast<uint32_t>(
         video_receiver_info.frame_height);
+    TRACE_EVENT2("webrtc_stats", "received_frame_width",
+                 "value", video_track_stats->frame_width.ValueToString(),
+                 "ssrc", video_receiver_info.ssrc());
+    TRACE_EVENT2("webrtc_stats", "received_frame_height",
+                 "value", video_track_stats->frame_width.ValueToString(),
+                 "ssrc", video_receiver_info.ssrc());
   }
   video_track_stats->frames_received = video_receiver_info.frames_received;
   // TODO(hbos): When we support receiving simulcast, this should be the total
@@ -467,6 +483,15 @@ ProduceMediaStreamTrackStatsFromVideoReceiverInfo(
                 video_receiver_info.frames_rendered);
   video_track_stats->frames_dropped = video_receiver_info.frames_received -
                                       video_receiver_info.frames_rendered;
+  TRACE_EVENT2("webrtc_stats", "frames_received",
+               "value", video_track_stats->frames_received.ValueToString(),
+               "ssrc", video_receiver_info.ssrc());
+  TRACE_EVENT2("webrtc_stats", "frames_decoded",
+               "value", video_track_stats->frames_decoded.ValueToString(),
+               "ssrc", video_receiver_info.ssrc());
+  TRACE_EVENT2("webrtc_stats", "frames_dropped",
+               "value", video_track_stats->frames_dropped.ValueToString(),
+               "ssrc", video_receiver_info.ssrc());

[hbos, 2017/07/11 13:37:13]

The "ssrc" is not a identifier of this report, you should use id() instead, and
dictionary type is probably of interest. See dictionaries in spec
https://w3c.github.io/webrtc-stats/#stats-dictionaries or rtcstats_objects.h.

See other comment, I think you want to trace by these categories:

getStats API / stats dictionary type / stats object id / member name / member
value
e.g. "getStats" / "track" / "xxx" / "famesDropped" / "10"

   return video_track_stats;
 }