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..229213c63ac4f68d2a550d2c5b031a1079337be8 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 {
 
@@ -751,6 +752,15 @@ void RTCStatsCollector::AddPartialResults_s(
     channel_name_pairs_.reset();
     track_media_info_map_.reset();
     track_to_id_.clear();
+    for (const RTCStats& stats : *cached_report_) {
+      for (const RTCStatsMemberInterface* member : stats.Members()) {
+        if (member->is_defined()) {
+          TRACE_EVENT_INSTANT2("webrtc_stats", member->name(),
+                               "value", member->ValueToString(),
+                               stats.type(), stats.id());

[hbos, 2017/07/12 11:26:51]

I think stats name might be wrong to have as trace name, because there are a few
cases where the same member name is used inside different stats dictionaries
even though they're not examples of the same thing. (Example: bytesSent is in
RTCSentRTPStreamStats, RTCDataChannelStats, RTCTransportStats and
RTCIceCandidatePairStats). Probably, the dictionary should be the name argument,
and the additional arguments be the sub-dictionary information, from higher
level information to lower level.

TRACE_EVENT_INSTANT2(
  "webrtc_stats",            // category
  stats.type(),              // name
  "id",                      // arg1_name
  stats.id(),                // arg1_value
  member->name(),            // arg2_name
  member->ValueToString());  // arg2_value

Or if "name" should fully identify an example of this particular metric and not
just the dictionary, then this should probably be the way to go:

TRACE_EVENT_INSTANT2(
  "webrtc_stats",            // category
  stats.type() + "." + member->name(),  // name
  "id",                      // arg1_name
  stats.id(),                // arg1_value
  "value",                   // arg2_name
  member->ValueToString());  // arg2_value

[ehmaldonado_webrtc, 2017/07/12 12:45:51]

Right. Done.

+        }
+      }
+    }
     DeliverCachedReport();
   }
 }