Collecting RTCIceCandidatePairStats.transport_id and improved unittests

webrtc/stats/rtcstats_unittest.cc

Index: webrtc/stats/rtcstats_unittest.cc
diff --git a/webrtc/stats/rtcstats_unittest.cc b/webrtc/stats/rtcstats_unittest.cc
index 78543557442823f7d50fde50203417d3577b5a36..6fe8dd90467f4623614382bb823fe276356e9e45 100644
--- a/webrtc/stats/rtcstats_unittest.cc
+++ b/webrtc/stats/rtcstats_unittest.cc
@@ -167,7 +167,7 @@ TEST(RTCStatsTest, EqualityOperator) {
   RTCTestStats empty_stats_different_id("testId2", 123);
   EXPECT_NE(empty_stats, empty_stats_different_id);
   RTCTestStats empty_stats_different_timestamp("testId", 321);
-  EXPECT_NE(empty_stats, empty_stats_different_timestamp);
+  EXPECT_EQ(empty_stats, empty_stats_different_timestamp);
 
   RTCChildStats child("childId", 42);
   RTCGrandChildStats grandchild("grandchildId", 42);