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..dcb417c885511989538a54756452f8ed7d2d95a2 100644
--- a/webrtc/pc/rtcstatscollector.cc
+++ b/webrtc/pc/rtcstatscollector.cc
@@ -24,12 +24,21 @@
 #include "webrtc/pc/peerconnection.h"
 #include "webrtc/pc/webrtcsession.h"
 #include "webrtc/rtc_base/checks.h"
+#include "webrtc/rtc_base/stringutils.h"
 #include "webrtc/rtc_base/timeutils.h"
+#include "webrtc/rtc_base/trace_event.h"
 
 namespace webrtc {
 
 namespace {
 
+std::string TraceNameFromStatsTypeAndMemberName(const char* stats_type,
+                                                const char* member_name) {
+  char buffer[80];
+  rtc::sprintfn(&buffer[0], sizeof(buffer), "%s.%s", stats_type, member_name);

[tommi, 2017/07/12 16:53:03]

You might want to add dchecks for the length of the constants

+  return buffer;
+}
+
 std::string RTCCertificateIDFromFingerprint(const std::string& fingerprint) {
   return "RTCCertificate_" + fingerprint;
 }
@@ -751,6 +760,20 @@ void RTCStatsCollector::AddPartialResults_s(
     channel_name_pairs_.reset();
     track_media_info_map_.reset();
     track_to_id_.clear();
+    // Trace WebRTC Stats when getStats is called on Javascript.
+    // This allows access to WebRTC stats from trace logs. To enable them,
+    // select the "webrtc_stats" category when recording traces.
+    for (const RTCStats& stats : *cached_report_) {
+      for (const RTCStatsMemberInterface* member : stats.Members()) {
+        if (member->is_defined()) {
+          TRACE_EVENT_INSTANT2("webrtc_stats",
+                               TraceNameFromStatsTypeAndMemberName(
+                                   stats.type(), member->name()).c_str(),

[tommi, 2017/07/12 16:53:03]

Have you checked if this is a concern?
https://cs.chromium.org/chromium/src/base/trace_event/common/trace_event_comm...

[ehmaldonado_webrtc, 2017/07/12 18:57:10]

Right, I missed that. :(

I think the easiest way would be to trace all events under a single trace name,
something like:

  TRACE_EVENT_INSTANT2("webrtc_stats", "webrtc_stats",
                       "value", member->ValueToString(),
                       "stat_info", "%s.%s.%s" % (
                           stats.name(), member->name(), stats.id())); 

(That's not valid C++, but you get the idea :P)

Otherwise I think we'll have to trace each stat separately, or define lots of
const char* so we can reference them.

What do you think? Maybe I'm missing something.

+                               "value", member->ValueToString(),
+                               "id", stats.id());
+        }
+      }
+    }
     DeliverCachedReport();
   }
 }