RTCStatsCollector: Utilize network thread to minimize thread hops.

webrtc/api/test/mock_webrtcsession.h

Index: webrtc/api/test/mock_webrtcsession.h
diff --git a/webrtc/api/test/mock_webrtcsession.h b/webrtc/api/test/mock_webrtcsession.h
index 108bdcaac09e78feb3ad588123f1750d846036e5..7fefad857d8883f495fde1133f5d891b086f9dd9 100644
--- a/webrtc/api/test/mock_webrtcsession.h
+++ b/webrtc/api/test/mock_webrtcsession.h
@@ -42,7 +42,8 @@ class MockWebRtcSession : public webrtc::WebRtcSession {
   // track.
   MOCK_METHOD2(GetLocalTrackIdBySsrc, bool(uint32_t, std::string*));
   MOCK_METHOD2(GetRemoteTrackIdBySsrc, bool(uint32_t, std::string*));
-  MOCK_METHOD1(GetTransportStats, bool(SessionStats*));
+  MOCK_METHOD1(GetStats,
+               std::unique_ptr<SessionStats>(const ChannelNamePairs&));
   MOCK_METHOD2(GetLocalCertificate,
                bool(const std::string& transport_name,
                     rtc::scoped_refptr<rtc::RTCCertificate>* certificate));