RTCStatsReport::AddStats DCHECKs that the ID is unique.

Previously it was allowed to call AddStats with stats of the same ID
multiple times.

This revealed a few things:
- Local and remote streams can have the same label.
  RTCMediaStreamStats's ID is updated to include "local"/"remote".
- The same certificate can show up multiple times (e.g. for local and
  remote in a loopback), so we skip creating RTCCertificateStats for the
  same certificate multiple times

BUG=chromium:627816

Review-Url: https://codereview.webrtc.org/2593503003
Cr-Commit-Position: refs/heads/master@{#15730}

webrtc/api/rtcstatscollector.cc

@@ -233,8 +233,17 @@ void ProduceCertificateStatsFromSSLCertificateStats(
   RTCCertificateStats* prev_certificate_stats = nullptr;
   for (const rtc::SSLCertificateStats* s = &certificate_stats; s;
        s = s->issuer.get()) {
+    std::string certificate_stats_id =
+        RTCCertificateIDFromFingerprint(s->fingerprint);
+    // It is possible for the same certificate to show up multiple times, e.g.
+    // if local and remote side use the same certificate in a loopback call.
+    // If the report already contains stats for this certificate, skip it.
+    if (report->Get(certificate_stats_id)) {
+      RTC_DCHECK_EQ(s, &certificate_stats);
+      break;
+    }
     RTCCertificateStats* certificate_stats = new RTCCertificateStats(
-        RTCCertificateIDFromFingerprint(s->fingerprint), timestamp_us);
+        certificate_stats_id, timestamp_us);
     certificate_stats->fingerprint = s->fingerprint;
     certificate_stats->fingerprint_algorithm = s->fingerprint_algorithm;
     certificate_stats->base64_certificate = s->base64_certificate;
@@ -288,8 +297,9 @@ void ProduceMediaStreamAndTrackStats(
     MediaStreamInterface* stream = streams->at(i);
 
     std::unique_ptr<RTCMediaStreamStats> stream_stats(
-        new RTCMediaStreamStats("RTCMediaStream_" + stream->label(),
-                                timestamp_us));
+        new RTCMediaStreamStats(
+            (is_local ? "RTCMediaStream_local_" : "RTCMediaStream_remote_") +
+            stream->label(), timestamp_us));
     stream_stats->stream_identifier = stream->label();
     stream_stats->track_ids = std::vector<std::string>();
     // Audio Tracks

webrtc/api/rtcstatscollector_unittest.cc

@@ -969,6 +969,7 @@ TEST_F(RTCStatsCollectorTest, CollectRTCIceCandidateStats) {
       *a_local_prflx.get();
   a_transport_channel_stats.connection_infos[1].remote_candidate =
       *a_remote_relay.get();
+  session_stats.transport_stats["a"].transport_name = "a";
   session_stats.transport_stats["a"].channel_stats.push_back(
       a_transport_channel_stats);
 
@@ -979,6 +980,7 @@ TEST_F(RTCStatsCollectorTest, CollectRTCIceCandidateStats) {
       *b_local.get();
   b_transport_channel_stats.connection_infos[0].remote_candidate =
       *b_remote.get();
+  session_stats.transport_stats["b"].transport_name = "b";
   session_stats.transport_stats["b"].channel_stats.push_back(
       b_transport_channel_stats);
 
@@ -1164,7 +1166,7 @@ TEST_F(RTCStatsCollectorTest,
   rtc::scoped_refptr<const RTCStatsReport> report = GetStatsReport();
 
   RTCMediaStreamStats expected_local_stream(
-      "RTCMediaStream_LocalStreamLabel", report->timestamp_us());
+      "RTCMediaStream_local_LocalStreamLabel", report->timestamp_us());
   expected_local_stream.stream_identifier = local_stream->label();
   expected_local_stream.track_ids = std::vector<std::string>();
   expected_local_stream.track_ids->push_back(
@@ -1175,7 +1177,7 @@ TEST_F(RTCStatsCollectorTest,
                 RTCMediaStreamStats>());
 
   RTCMediaStreamStats expected_remote_stream(
-      "RTCMediaStream_RemoteStreamLabel", report->timestamp_us());
+      "RTCMediaStream_remote_RemoteStreamLabel", report->timestamp_us());
   expected_remote_stream.stream_identifier = remote_stream->label();
   expected_remote_stream.track_ids = std::vector<std::string>();
   expected_remote_stream.track_ids->push_back(
@@ -1301,7 +1303,7 @@ TEST_F(RTCStatsCollectorTest,
   rtc::scoped_refptr<const RTCStatsReport> report = GetStatsReport();
 
   RTCMediaStreamStats expected_local_stream(
-      "RTCMediaStream_LocalStreamLabel", report->timestamp_us());
+      "RTCMediaStream_local_LocalStreamLabel", report->timestamp_us());
   expected_local_stream.stream_identifier = local_stream->label();
   expected_local_stream.track_ids = std::vector<std::string>();
   expected_local_stream.track_ids->push_back(
@@ -1312,7 +1314,7 @@ TEST_F(RTCStatsCollectorTest,
                 RTCMediaStreamStats>());
 
   RTCMediaStreamStats expected_remote_stream(
-      "RTCMediaStream_RemoteStreamLabel", report->timestamp_us());
+      "RTCMediaStream_remote_RemoteStreamLabel", report->timestamp_us());
   expected_remote_stream.stream_identifier = remote_stream->label();
   expected_remote_stream.track_ids = std::vector<std::string>();
   expected_remote_stream.track_ids->push_back(

webrtc/api/stats/rtcstatsreport.h

@@ -58,7 +58,7 @@ class RTCStatsReport : public rtc::RefCountInterface {
   RTCStatsReport(const RTCStatsReport& other) = delete;
 
   int64_t timestamp_us() const { return timestamp_us_; }
-  bool AddStats(std::unique_ptr<const RTCStats> stats);
+  void AddStats(std::unique_ptr<const RTCStats> stats);
   const RTCStats* Get(const std::string& id) const;
   size_t size() const { return stats_.size(); }
 

webrtc/stats/rtcstatsreport.cc

@@ -69,9 +69,12 @@ RTCStatsReport::RTCStatsReport(int64_t timestamp_us)
 RTCStatsReport::~RTCStatsReport() {
 }
 
-bool RTCStatsReport::AddStats(std::unique_ptr<const RTCStats> stats) {
-  return !stats_.insert(std::make_pair(std::string(stats->id()),
-                        std::move(stats))).second;
+void RTCStatsReport::AddStats(std::unique_ptr<const RTCStats> stats) {
+  auto result = stats_.insert(std::make_pair(std::string(stats->id()),
+                              std::move(stats)));
+  RTC_DCHECK(result.second) <<
+      "A stats object with ID " << result.first->second->id() << " is already "
+      "present in this stats report.";
 }
 
 const RTCStats* RTCStatsReport::Get(const std::string& id) const {