Make StatsCollector depend on always having a valid session pointer.

This is required since the session pointer is currently used on multiple threads but there's no synchronization code to guard it.
I'm removing the set_session() method and session() getter since they would cause problems if used without synchronization.

This is a reland of an already reviewed cl that got reverted by mistake.

TBR=xians@google.com

Review URL: https://webrtc-codereview.appspot.com/13959004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6677 4adac7df-926f-26a2-2b94-8c16560cd09d

talk/app/webrtc/peerconnection.cc

@@ -373,7 +373,7 @@ bool PeerConnection::DoInitialize(
                                    mediastream_signaling_.get()));
   stream_handler_container_.reset(new MediaStreamHandlerContainer(
       session_.get(), session_.get()));
-  stats_.set_session(session_.get());
+  stats_.reset(new StatsCollector(session_.get()));
 
   // Initialize the WebRtcSession. It creates transport channels etc.
   if (!session_->Initialize(factory_->options(), constraints,
@@ -410,7 +410,7 @@ bool PeerConnection::AddStream(MediaStreamInterface* local_stream,
   if (!mediastream_signaling_->AddLocalStream(local_stream)) {
     return false;
   }
-  stats_.AddStream(local_stream);
+  stats_->AddStream(local_stream);
   observer_->OnRenegotiationNeeded();
   return true;
 }
@@ -451,9 +451,9 @@ bool PeerConnection::GetStats(StatsObserver* observer,
     return false;
   }
 
-  stats_.UpdateStats(level);
+  stats_->UpdateStats(level);
   talk_base::scoped_ptr<GetStatsMsg> msg(new GetStatsMsg(observer));
-  if (!stats_.GetStats(track, &(msg->reports))) {
+  if (!stats_->GetStats(track, &(msg->reports))) {
     return false;
   }
   signaling_thread()->Post(this, MSG_GETSTATS, msg.release());
@@ -534,7 +534,7 @@ void PeerConnection::SetLocalDescription(
   }
   // Update stats here so that we have the most recent stats for tracks and
   // streams that might be removed by updating the session description.
-  stats_.UpdateStats(kStatsOutputLevelStandard);
+  stats_->UpdateStats(kStatsOutputLevelStandard);
   std::string error;
   if (!session_->SetLocalDescription(desc, &error)) {
     PostSetSessionDescriptionFailure(observer, error);
@@ -557,7 +557,7 @@ void PeerConnection::SetRemoteDescription(
   }
   // Update stats here so that we have the most recent stats for tracks and
   // streams that might be removed by updating the session description.
-  stats_.UpdateStats(kStatsOutputLevelStandard);
+  stats_->UpdateStats(kStatsOutputLevelStandard);
   std::string error;
   if (!session_->SetRemoteDescription(desc, &error)) {
     PostSetSessionDescriptionFailure(observer, error);
@@ -649,7 +649,7 @@ const SessionDescriptionInterface* PeerConnection::remote_description() const {
 void PeerConnection::Close() {
   // Update stats here so that we have the most recent stats for tracks and
   // streams before the channels are closed.
-  stats_.UpdateStats(kStatsOutputLevelStandard);
+  stats_->UpdateStats(kStatsOutputLevelStandard);
 
   session_->Terminate();
 }
@@ -713,7 +713,7 @@ void PeerConnection::OnMessage(talk_base::Message* msg) {
 }
 
 void PeerConnection::OnAddRemoteStream(MediaStreamInterface* stream) {
-  stats_.AddStream(stream);
+  stats_->AddStream(stream);
   observer_->OnAddStream(stream);
 }
 
@@ -754,7 +754,7 @@ void PeerConnection::OnAddLocalAudioTrack(MediaStreamInterface* stream,
                                           AudioTrackInterface* audio_track,
                                           uint32 ssrc) {
   stream_handler_container_->AddLocalAudioTrack(stream, audio_track, ssrc);
-  stats_.AddLocalAudioTrack(audio_track, ssrc);
+  stats_->AddLocalAudioTrack(audio_track, ssrc);
 }
 void PeerConnection::OnAddLocalVideoTrack(MediaStreamInterface* stream,
                                           VideoTrackInterface* video_track,
@@ -766,7 +766,7 @@ void PeerConnection::OnRemoveLocalAudioTrack(MediaStreamInterface* stream,
                                              AudioTrackInterface* audio_track,
                                              uint32 ssrc) {
   stream_handler_container_->RemoveLocalTrack(stream, audio_track);
-  stats_.RemoveLocalAudioTrack(audio_track, ssrc);
+  stats_->RemoveLocalAudioTrack(audio_track, ssrc);
 }
 
 void PeerConnection::OnRemoveLocalVideoTrack(MediaStreamInterface* stream,

talk/app/webrtc/peerconnection.h

@@ -196,7 +196,7 @@ class PeerConnection : public PeerConnectionInterface,
   talk_base::scoped_ptr<WebRtcSession> session_;
   talk_base::scoped_ptr<MediaStreamSignaling> mediastream_signaling_;
   talk_base::scoped_ptr<MediaStreamHandlerContainer> stream_handler_container_;
-  StatsCollector stats_;
+  talk_base::scoped_ptr<StatsCollector> stats_;
 };
 
 }  // namespace webrtc

talk/app/webrtc/statscollector.cc

@@ -528,8 +528,12 @@ void ExtractStatsFromList(const std::vector<T>& data,
 
 }  // namespace
 
-StatsCollector::StatsCollector()
-    : session_(NULL), stats_gathering_started_(0) {
+StatsCollector::StatsCollector(WebRtcSession* session)
+    : session_(session), stats_gathering_started_(0) {
+  ASSERT(session_);
+}
+
+StatsCollector::~StatsCollector() {
 }
 
 // Adds a MediaStream with tracks that can be used as a |selector| in a call
@@ -1063,14 +1067,14 @@ void StatsCollector::UpdateReportFromAudioTrack(AudioTrackInterface* track,
 bool StatsCollector::GetTrackIdBySsrc(uint32 ssrc, std::string* track_id,
                                       TrackDirection direction) {
   if (direction == kSending) {
-    if (!session()->GetLocalTrackIdBySsrc(ssrc, track_id)) {
+    if (!session_->GetLocalTrackIdBySsrc(ssrc, track_id)) {
       LOG(LS_WARNING) << "The SSRC " << ssrc
                       << " is not associated with a sending track";
       return false;
     }
   } else {
     ASSERT(direction == kReceiving);
-    if (!session()->GetRemoteTrackIdBySsrc(ssrc, track_id)) {
+    if (!session_->GetRemoteTrackIdBySsrc(ssrc, track_id)) {
       LOG(LS_WARNING) << "The SSRC " << ssrc
                       << " is not associated with a receiving track";
       return false;

talk/app/webrtc/statscollector.h

@@ -49,13 +49,10 @@ class StatsCollector {
     kReceiving,
   };
 
-  StatsCollector();
-
-  // Register the session Stats should operate on.
-  // Set to NULL if the session has ended.
-  void set_session(WebRtcSession* session) {
-    session_ = session;
-  }
+  // The caller is responsible for ensuring that the session outlives the
+  // StatsCollector instance.
+  explicit StatsCollector(WebRtcSession* session);
+  virtual ~StatsCollector();
 
   // Adds a MediaStream with tracks that can be used as a |selector| in a call
   // to GetStats.
@@ -110,7 +107,6 @@ class StatsCollector {
   void ExtractVideoInfo(PeerConnectionInterface::StatsOutputLevel level);
   double GetTimeNow();
   void BuildSsrcToTransportId();
-  WebRtcSession* session() { return session_; }
   webrtc::StatsReport* GetOrCreateReport(const std::string& type,
                                          const std::string& id,
                                          TrackDirection direction);
@@ -131,7 +127,7 @@ class StatsCollector {
   // A map from the report id to the report.
   std::map<std::string, StatsReport> reports_;
   // Raw pointer to the session the statistics are gathered from.
-  WebRtcSession* session_;
+  WebRtcSession* const session_;
   double stats_gathering_started_;
   cricket::ProxyTransportMap proxy_to_transport_;
 

talk/app/webrtc/statscollector_unittest.cc

@@ -514,7 +514,6 @@ class StatsCollectorTest : public testing::Test {
     // A track can't have both sender report and recv report at the same time
     // for now, this might change in the future though.
     ASSERT((voice_sender_info == NULL) ^ (voice_receiver_info == NULL));
-    stats->set_session(&session_);
 
     // Instruct the session to return stats containing the transport channel.
     InitSessionStats(vc_name);
@@ -580,9 +579,8 @@ class StatsCollectorTest : public testing::Test {
                               const std::vector<std::string>& local_ders,
                               const talk_base::FakeSSLCertificate& remote_cert,
                               const std::vector<std::string>& remote_ders) {
-    webrtc::StatsCollector stats;  // Implementation under test.
+    webrtc::StatsCollector stats(&session_);  // Implementation under test.
     StatsReports reports;  // returned values.
-    stats.set_session(&session_);
 
     // Fake stats to process.
     cricket::TransportChannelStats channel_stats;
@@ -667,7 +665,7 @@ class StatsCollectorTest : public testing::Test {
 
 // This test verifies that 64-bit counters are passed successfully.
 TEST_F(StatsCollectorTest, BytesCounterHandles64Bits) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   MockVideoMediaChannel* media_channel = new MockVideoMediaChannel();
   cricket::VideoChannel video_channel(talk_base::Thread::Current(),
       media_engine_, media_channel, &session_, "", false, NULL);
@@ -678,7 +676,6 @@ TEST_F(StatsCollectorTest, BytesCounterHandles64Bits) {
   const int64 kBytesSent = 12345678901234LL;
   const std::string kBytesSentString("12345678901234");
 
-  stats.set_session(&session_);
   AddOutgoingVideoTrackStats();
   stats.AddStream(stream_);
 
@@ -700,7 +697,7 @@ TEST_F(StatsCollectorTest, BytesCounterHandles64Bits) {
 
 // Test that BWE information is reported via stats.
 TEST_F(StatsCollectorTest, BandwidthEstimationInfoIsReported) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   MockVideoMediaChannel* media_channel = new MockVideoMediaChannel();
   cricket::VideoChannel video_channel(talk_base::Thread::Current(),
       media_engine_, media_channel, &session_, "", false, NULL);
@@ -712,7 +709,6 @@ TEST_F(StatsCollectorTest, BandwidthEstimationInfoIsReported) {
   const int64 kBytesSent = 12345678901234LL;
   const std::string kBytesSentString("12345678901234");
 
-  stats.set_session(&session_);
   AddOutgoingVideoTrackStats();
   stats.AddStream(stream_);
 
@@ -743,9 +739,8 @@ TEST_F(StatsCollectorTest, BandwidthEstimationInfoIsReported) {
 // This test verifies that an object of type "googSession" always
 // exists in the returned stats.
 TEST_F(StatsCollectorTest, SessionObjectExists) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   StatsReports reports;  // returned values.
-  stats.set_session(&session_);
   EXPECT_CALL(session_, video_channel()).WillRepeatedly(ReturnNull());
   EXPECT_CALL(session_, voice_channel()).WillRepeatedly(ReturnNull());
   stats.UpdateStats(PeerConnectionInterface::kStatsOutputLevelStandard);
@@ -758,9 +753,8 @@ TEST_F(StatsCollectorTest, SessionObjectExists) {
 // This test verifies that only one object of type "googSession" exists
 // in the returned stats.
 TEST_F(StatsCollectorTest, OnlyOneSessionObjectExists) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   StatsReports reports;  // returned values.
-  stats.set_session(&session_);
   EXPECT_CALL(session_, video_channel()).WillRepeatedly(ReturnNull());
   EXPECT_CALL(session_, voice_channel()).WillRepeatedly(ReturnNull());
   stats.UpdateStats(PeerConnectionInterface::kStatsOutputLevelStandard);
@@ -777,18 +771,15 @@ TEST_F(StatsCollectorTest, OnlyOneSessionObjectExists) {
 // This test verifies that the empty track report exists in the returned stats
 // without calling StatsCollector::UpdateStats.
 TEST_F(StatsCollectorTest, TrackObjectExistsWithoutUpdateStats) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   MockVideoMediaChannel* media_channel = new MockVideoMediaChannel();
   cricket::VideoChannel video_channel(talk_base::Thread::Current(),
       media_engine_, media_channel, &session_, "", false, NULL);
   AddOutgoingVideoTrackStats();
   stats.AddStream(stream_);
 
-  stats.set_session(&session_);
-
-  StatsReports reports;
-
   // Verfies the existence of the track report.
+  StatsReports reports;
   stats.GetStats(NULL, &reports);
   EXPECT_EQ((size_t)1, reports.size());
   EXPECT_EQ(std::string(StatsReport::kStatsReportTypeTrack),
@@ -804,17 +795,13 @@ TEST_F(StatsCollectorTest, TrackObjectExistsWithoutUpdateStats) {
 // This test verifies that the empty track report exists in the returned stats
 // when StatsCollector::UpdateStats is called with ssrc stats.
 TEST_F(StatsCollectorTest, TrackAndSsrcObjectExistAfterUpdateSsrcStats) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   MockVideoMediaChannel* media_channel = new MockVideoMediaChannel();
   cricket::VideoChannel video_channel(talk_base::Thread::Current(),
       media_engine_, media_channel, &session_, "", false, NULL);
   AddOutgoingVideoTrackStats();
   stats.AddStream(stream_);
 
-  stats.set_session(&session_);
-
-  StatsReports reports;
-
   // Constructs an ssrc stats update.
   cricket::VideoSenderInfo video_sender_info;
   cricket::VideoMediaInfo stats_read;
@@ -832,6 +819,7 @@ TEST_F(StatsCollectorTest, TrackAndSsrcObjectExistAfterUpdateSsrcStats) {
                     Return(true)));
 
   stats.UpdateStats(PeerConnectionInterface::kStatsOutputLevelStandard);
+  StatsReports reports;
   stats.GetStats(NULL, &reports);
   // |reports| should contain at least one session report, one track report,
   // and one ssrc report.
@@ -861,7 +849,7 @@ TEST_F(StatsCollectorTest, TrackAndSsrcObjectExistAfterUpdateSsrcStats) {
 // This test verifies that an SSRC object has the identifier of a Transport
 // stats object, and that this transport stats object exists in stats.
 TEST_F(StatsCollectorTest, TransportObjectLinkedFromSsrcObject) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   MockVideoMediaChannel* media_channel = new MockVideoMediaChannel();
   // The content_name known by the video channel.
   const std::string kVcName("vcname");
@@ -870,10 +858,6 @@ TEST_F(StatsCollectorTest, TransportObjectLinkedFromSsrcObject) {
   AddOutgoingVideoTrackStats();
   stats.AddStream(stream_);
 
-  stats.set_session(&session_);
-
-  StatsReports reports;
-
   // Constructs an ssrc stats update.
   cricket::VideoSenderInfo video_sender_info;
   cricket::VideoMediaInfo stats_read;
@@ -896,6 +880,7 @@ TEST_F(StatsCollectorTest, TransportObjectLinkedFromSsrcObject) {
                             Return(true)));
 
   stats.UpdateStats(PeerConnectionInterface::kStatsOutputLevelStandard);
+  StatsReports reports;
   stats.GetStats(NULL, &reports);
   std::string transport_id = ExtractStatsValue(
       StatsReport::kStatsReportTypeSsrc,
@@ -910,7 +895,7 @@ TEST_F(StatsCollectorTest, TransportObjectLinkedFromSsrcObject) {
 // This test verifies that a remote stats object will not be created for
 // an outgoing SSRC where remote stats are not returned.
 TEST_F(StatsCollectorTest, RemoteSsrcInfoIsAbsent) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   MockVideoMediaChannel* media_channel = new MockVideoMediaChannel();
   // The content_name known by the video channel.
   const std::string kVcName("vcname");
@@ -919,8 +904,6 @@ TEST_F(StatsCollectorTest, RemoteSsrcInfoIsAbsent) {
   AddOutgoingVideoTrackStats();
   stats.AddStream(stream_);
 
-  stats.set_session(&session_);
-
   EXPECT_CALL(session_, video_channel()).WillRepeatedly(ReturnNull());
   EXPECT_CALL(session_, voice_channel()).WillRepeatedly(ReturnNull());
 
@@ -935,7 +918,7 @@ TEST_F(StatsCollectorTest, RemoteSsrcInfoIsAbsent) {
 // This test verifies that a remote stats object will be created for
 // an outgoing SSRC where stats are returned.
 TEST_F(StatsCollectorTest, RemoteSsrcInfoIsPresent) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   MockVideoMediaChannel* media_channel = new MockVideoMediaChannel();
   // The content_name known by the video channel.
   const std::string kVcName("vcname");
@@ -944,10 +927,6 @@ TEST_F(StatsCollectorTest, RemoteSsrcInfoIsPresent) {
   AddOutgoingVideoTrackStats();
   stats.AddStream(stream_);
 
-  stats.set_session(&session_);
-
-  StatsReports reports;
-
   // Instruct the session to return stats containing the transport channel.
   InitSessionStats(kVcName);
   EXPECT_CALL(session_, GetStats(_))
@@ -972,6 +951,7 @@ TEST_F(StatsCollectorTest, RemoteSsrcInfoIsPresent) {
                           Return(true)));
 
   stats.UpdateStats(PeerConnectionInterface::kStatsOutputLevelStandard);
+  StatsReports reports;
   stats.GetStats(NULL, &reports);
 
   const StatsReport* remote_report = FindNthReportByType(reports,
@@ -983,17 +963,13 @@ TEST_F(StatsCollectorTest, RemoteSsrcInfoIsPresent) {
 // This test verifies that the empty track report exists in the returned stats
 // when StatsCollector::UpdateStats is called with ssrc stats.
 TEST_F(StatsCollectorTest, ReportsFromRemoteTrack) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   MockVideoMediaChannel* media_channel = new MockVideoMediaChannel();
   cricket::VideoChannel video_channel(talk_base::Thread::Current(),
       media_engine_, media_channel, &session_, "", false, NULL);
   AddIncomingVideoTrackStats();
   stats.AddStream(stream_);
 
-  stats.set_session(&session_);
-
-  StatsReports reports;
-
   // Constructs an ssrc stats update.
   cricket::VideoReceiverInfo video_receiver_info;
   cricket::VideoMediaInfo stats_read;
@@ -1011,6 +987,7 @@ TEST_F(StatsCollectorTest, ReportsFromRemoteTrack) {
                       Return(true)));
 
   stats.UpdateStats(PeerConnectionInterface::kStatsOutputLevelStandard);
+  StatsReports reports;
   stats.GetStats(NULL, &reports);
   // |reports| should contain at least one session report, one track report,
   // and one ssrc report.
@@ -1069,9 +1046,8 @@ TEST_F(StatsCollectorTest, ChainlessCertificateReportsCreated) {
 // This test verifies that the stats are generated correctly when no
 // transport is present.
 TEST_F(StatsCollectorTest, NoTransport) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   StatsReports reports;  // returned values.
-  stats.set_session(&session_);
 
   // Fake stats to process.
   cricket::TransportChannelStats channel_stats;
@@ -1116,9 +1092,8 @@ TEST_F(StatsCollectorTest, NoTransport) {
 // This test verifies that the stats are generated correctly when the transport
 // does not have any certificates.
 TEST_F(StatsCollectorTest, NoCertificates) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   StatsReports reports;  // returned values.
-  stats.set_session(&session_);
 
   // Fake stats to process.
   cricket::TransportChannelStats channel_stats;
@@ -1185,13 +1160,11 @@ TEST_F(StatsCollectorTest, UnsupportedDigestIgnored) {
 // Verifies the correct optons are passed to the VideoMediaChannel when using
 // verbose output level.
 TEST_F(StatsCollectorTest, StatsOutputLevelVerbose) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   MockVideoMediaChannel* media_channel = new MockVideoMediaChannel();
   cricket::VideoChannel video_channel(talk_base::Thread::Current(),
       media_engine_, media_channel, &session_, "", false, NULL);
-  stats.set_session(&session_);
 
-  StatsReports reports;  // returned values.
   cricket::VideoMediaInfo stats_read;
   cricket::BandwidthEstimationInfo bwe;
   bwe.total_received_propagation_delta_ms = 10;
@@ -1214,6 +1187,7 @@ TEST_F(StatsCollectorTest, StatsOutputLevelVerbose) {
                     Return(true)));
 
   stats.UpdateStats(PeerConnectionInterface::kStatsOutputLevelDebug);
+  StatsReports reports;  // returned values.
   stats.GetStats(NULL, &reports);
   std::string result = ExtractBweStatsValue(
       reports, "googReceivedPacketGroupPropagationDeltaSumDebug");
@@ -1229,7 +1203,7 @@ TEST_F(StatsCollectorTest, StatsOutputLevelVerbose) {
 // This test verifies that a local stats object can get statistics via
 // AudioTrackInterface::GetStats() method.
 TEST_F(StatsCollectorTest, GetStatsFromLocalAudioTrack) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   MockVoiceMediaChannel* media_channel = new MockVoiceMediaChannel();
   // The content_name known by the voice channel.
   const std::string kVcName("vcname");
@@ -1258,7 +1232,7 @@ TEST_F(StatsCollectorTest, GetStatsFromLocalAudioTrack) {
 // This test verifies that audio receive streams populate stats reports
 // correctly.
 TEST_F(StatsCollectorTest, GetStatsFromRemoteStream) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   MockVoiceMediaChannel* media_channel = new MockVoiceMediaChannel();
   // The content_name known by the voice channel.
   const std::string kVcName("vcname");
@@ -1281,7 +1255,7 @@ TEST_F(StatsCollectorTest, GetStatsFromRemoteStream) {
 // This test verifies that a local stats object won't update its statistics
 // after a RemoveLocalAudioTrack() call.
 TEST_F(StatsCollectorTest, GetStatsAfterRemoveAudioStream) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   MockVoiceMediaChannel* media_channel = new MockVoiceMediaChannel();
   // The content_name known by the voice channel.
   const std::string kVcName("vcname");
@@ -1291,8 +1265,6 @@ TEST_F(StatsCollectorTest, GetStatsAfterRemoveAudioStream) {
   stats.AddStream(stream_);
   stats.AddLocalAudioTrack(audio_track_.get(), kSsrcOfTrack);
 
-  stats.set_session(&session_);
-
   // Instruct the session to return stats containing the transport channel.
   InitSessionStats(kVcName);
   EXPECT_CALL(session_, GetStats(_))
@@ -1337,7 +1309,7 @@ TEST_F(StatsCollectorTest, GetStatsAfterRemoveAudioStream) {
 // This test verifies that when ongoing and incoming audio tracks are using
 // the same ssrc, they populate stats reports correctly.
 TEST_F(StatsCollectorTest, LocalAndRemoteTracksWithSameSsrc) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   MockVoiceMediaChannel* media_channel = new MockVoiceMediaChannel();
   // The content_name known by the voice channel.
   const std::string kVcName("vcname");
@@ -1359,8 +1331,6 @@ TEST_F(StatsCollectorTest, LocalAndRemoteTracksWithSameSsrc) {
   remote_stream->AddTrack(remote_track);
   stats.AddStream(remote_stream);
 
-  stats.set_session(&session_);
-
   // Instruct the session to return stats containing the transport channel.
   InitSessionStats(kVcName);
   EXPECT_CALL(session_, GetStats(_))
@@ -1417,7 +1387,7 @@ TEST_F(StatsCollectorTest, LocalAndRemoteTracksWithSameSsrc) {
 // TODO(xians): Figure out if it is possible to encapsulate the setup and
 // avoid duplication of code in test cases.
 TEST_F(StatsCollectorTest, TwoLocalTracksWithSameSsrc) {
-  webrtc::StatsCollector stats;  // Implementation under test.
+  webrtc::StatsCollector stats(&session_);  // Implementation under test.
   MockVoiceMediaChannel* media_channel = new MockVoiceMediaChannel();
   // The content_name known by the voice channel.
   const std::string kVcName("vcname");