RTCRTPStreamStats.ssrc changed type to uint32_t.

As per PR: https://github.com/w3c/webrtc-stats/pull/157

BUG=webrtc:7065, webrtc:7066

Review-Url: https://codereview.webrtc.org/2675583003
Cr-Original-Commit-Position: refs/heads/master@{#16471}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 3443bb75a08811a16fd2dd406f72878703f4a861
diff --git a/pc/rtcstatscollector_unittest.cc b/pc/rtcstatscollector_unittest.cc
index 178deee..8118971 100644
--- a/pc/rtcstatscollector_unittest.cc
+++ b/pc/rtcstatscollector_unittest.cc
@@ -1722,7 +1722,7 @@
 
   RTCInboundRTPStreamStats expected_audio(
       "RTCInboundRTPAudioStream_1", report->timestamp_us());
-  expected_audio.ssrc = "1";
+  expected_audio.ssrc = 1;
   expected_audio.is_remote = false;
   expected_audio.media_type = "audio";
   expected_audio.track_id =
@@ -1805,7 +1805,7 @@
 
   RTCInboundRTPStreamStats expected_video(
       "RTCInboundRTPVideoStream_1", report->timestamp_us());
-  expected_video.ssrc = "1";
+  expected_video.ssrc = 1;
   expected_video.is_remote = false;
   expected_video.media_type = "video";
   expected_video.track_id =
@@ -1885,7 +1885,7 @@
 
   RTCOutboundRTPStreamStats expected_audio(
       "RTCOutboundRTPAudioStream_1", report->timestamp_us());
-  expected_audio.ssrc = "1";
+  expected_audio.ssrc = 1;
   expected_audio.is_remote = false;
   expected_audio.media_type = "audio";
   expected_audio.track_id =
@@ -1965,7 +1965,7 @@
 
   RTCOutboundRTPStreamStats expected_video(
       "RTCOutboundRTPVideoStream_1", report->timestamp_us());
-  expected_video.ssrc = "1";
+  expected_video.ssrc = 1;
   expected_video.is_remote = false;
   expected_video.media_type = "video";
   expected_video.track_id =
@@ -2056,7 +2056,7 @@
 
   RTCOutboundRTPStreamStats expected_audio(
       "RTCOutboundRTPAudioStream_1", report->timestamp_us());
-  expected_audio.ssrc = "1";
+  expected_audio.ssrc = 1;
   expected_audio.is_remote = false;
   expected_audio.media_type = "audio";
   expected_audio.transport_id = "RTCTransport_TransportName_" +
@@ -2073,7 +2073,7 @@
 
   RTCOutboundRTPStreamStats expected_video(
       "RTCOutboundRTPVideoStream_1", report->timestamp_us());
-  expected_video.ssrc = "1";
+  expected_video.ssrc = 1;
   expected_video.is_remote = false;
   expected_video.media_type = "video";
   expected_video.transport_id = "RTCTransport_TransportName_" +