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..c0a9f442b295e81bae406ca569c167fe792efc58 100644
--- a/webrtc/pc/rtcstatscollector.cc
+++ b/webrtc/pc/rtcstatscollector.cc
@@ -24,12 +24,26 @@
 #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 {
 
+const int kStatTypeMemberNameAndIdMaxLen = 120;

[ehmaldonado_webrtc, 2017/07/13 09:40:42]

Henrik, do you think 120 chars will be enough?

[hbos, 2017/07/18 08:55:08]

Yes. In the very unlikely case that it won't be in the future we'll notice
thanks to the DCHECK.

[hbos, 2017/07/18 10:09:48]

Oh sorry, I forgot about the length of the ID, and while typically short the
RTCCertificate IDs are a special case where it's really long! We should make the
buffer longer. I suspect the DCHECK will fail on rtcstats_integrationtest.cc.

Example string for certificates:

certificate.fingerprintAlgorithm.FE:C9:98:64:F3:3C:3E:A2:1A:ED:00:2D:17:18:6A:F2:2D:27:E5:BC:89:DE:67:11:83:B6:D6:5D:40:5E:FB:A3

That's 128 characters long! Let's go ahead and make
kStatTypeMemberNameAndIdMaxLen = 512 for plenty of margin (which is fine since
it's on the stack).

[hbos, 2017/07/18 10:11:58]

Or rather
"certificate.fingerprintAlgorithm.RTCCertificate_FE:C9:98:64:F3:3C:3E:A2:1A:ED:00:2D:17:18:6A:F2:2D:27:E5:BC:89:DE:67:11:83:B6:D6:5D:40:5E:FB:A3",
even longer. (And yeah, ':' can't be separator either.)

+
+std::string GetStatTypeMemberNameAndId(const RTCStats& stats,
+                                       const RTCStatsMemberInterface* member) {
+  RTC_DCHECK(strlen(stats.type()) + strlen(member->name())
+             + stats.id().size() + 3 < kStatTypeMemberNameAndIdMaxLen);
+  char buffer[kStatTypeMemberNameAndIdMaxLen];
+  rtc::sprintfn(&buffer[0], sizeof(buffer), "%s.%s.%s", stats.type(),
+                member->name(), stats.id().c_str());
+  return buffer;
+}
+
 std::string RTCCertificateIDFromFingerprint(const std::string& fingerprint) {
   return "RTCCertificate_" + fingerprint;
 }
@@ -751,6 +765,19 @@ 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", "webrtc_stats",
+                               "value", member->ValueToString(),
+                               "type+name+id", GetStatTypeMemberNameAndId(

[hbos, 2017/07/18 08:55:08]

nit: How about "type.name.id" to match the format of GetStatTypeMemberNameAndId?
Or if the '.' has special meaning somewhere we could use a different separator
like ' '. type, name and ids so far only use A-Z, a-z, _, -, 0-9, anything else
could be a separator.

+                                   stats, member));
+        }
+      }
+    }
     DeliverCachedReport();
   }
 }