Initialize the rtp_stream_id field added by https://codereview.chromium.org/2307653002/.

media/cast/net/cast_transport_config.cc

Index: media/cast/net/cast_transport_config.cc
diff --git a/media/cast/net/cast_transport_config.cc b/media/cast/net/cast_transport_config.cc
index 77f3cde68c81f35990edee1704b7321fa893b522..e3ee10b08bd9ae4ad079baa11b23984648e67116 100644
--- a/media/cast/net/cast_transport_config.cc
+++ b/media/cast/net/cast_transport_config.cc
@@ -8,7 +8,10 @@ namespace media {
 namespace cast {
 
 CastTransportRtpConfig::CastTransportRtpConfig()
-    : ssrc(0), feedback_ssrc(0), rtp_payload_type(RtpPayloadType::UNKNOWN) {}
+    : rtp_stream_id(0),
+      ssrc(0),
+      feedback_ssrc(0),
+      rtp_payload_type(RtpPayloadType::UNKNOWN) {}
 
 CastTransportRtpConfig::~CastTransportRtpConfig() {}