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/api/stats/rtcstats_objects.h b/api/stats/rtcstats_objects.h
index 6c24d67..29fcfaf 100644
--- a/api/stats/rtcstats_objects.h
+++ b/api/stats/rtcstats_objects.h
@@ -302,7 +302,7 @@
   RTCRTPStreamStats(const RTCRTPStreamStats& other);
   ~RTCRTPStreamStats() override;
 
-  RTCStatsMember<std::string> ssrc;
+  RTCStatsMember<uint32_t> ssrc;
   // TODO(hbos): When the remote case is supported |RTCStatsCollector| needs to
   // set this. crbug.com/657855, 657856
   RTCStatsMember<std::string> associate_stats_id;
diff --git a/pc/rtcstatscollector.cc b/pc/rtcstatscollector.cc
index 38b729a..d1602d6 100644
--- a/pc/rtcstatscollector.cc
+++ b/pc/rtcstatscollector.cc
@@ -196,7 +196,7 @@
     const cricket::MediaReceiverInfo& media_receiver_info,
     RTCInboundRTPStreamStats* inbound_stats) {
   RTC_DCHECK(inbound_stats);
-  inbound_stats->ssrc = rtc::ToString<>(media_receiver_info.ssrc());
+  inbound_stats->ssrc = media_receiver_info.ssrc();
   // TODO(hbos): Support the remote case. crbug.com/657855
   inbound_stats->is_remote = false;
   inbound_stats->packets_received =
@@ -252,7 +252,7 @@
     const cricket::MediaSenderInfo& media_sender_info,
     RTCOutboundRTPStreamStats* outbound_stats) {
   RTC_DCHECK(outbound_stats);
-  outbound_stats->ssrc = rtc::ToString<>(media_sender_info.ssrc());
+  outbound_stats->ssrc = media_sender_info.ssrc();
   // TODO(hbos): Support the remote case. crbug.com/657856
   outbound_stats->is_remote = false;
   outbound_stats->packets_sent =
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_" +