Add Cast PLI support on sender side.

media/cast/net/rtcp/rtcp_defines.cc

Index: media/cast/net/rtcp/rtcp_defines.cc
diff --git a/media/cast/net/rtcp/rtcp_defines.cc b/media/cast/net/rtcp/rtcp_defines.cc
index f7a1a6cab41dc00a398e32f03ce4f208210f923d..fd3e09b08cc3d1a4053643b1b089eff64724f053 100644
--- a/media/cast/net/rtcp/rtcp_defines.cc
+++ b/media/cast/net/rtcp/rtcp_defines.cc
@@ -10,11 +10,14 @@ namespace media {
 namespace cast {
 
 RtcpCastMessage::RtcpCastMessage(uint32_t ssrc)
-    : media_ssrc(ssrc), ack_frame_id(0u), target_delay_ms(0) {}
+    : remote_ssrc(ssrc), ack_frame_id(0u), target_delay_ms(0) {}
 RtcpCastMessage::RtcpCastMessage()
-    : media_ssrc(0), ack_frame_id(0u), target_delay_ms(0) {}
+    : remote_ssrc(0), ack_frame_id(0u), target_delay_ms(0) {}
 RtcpCastMessage::~RtcpCastMessage() {}
 
+RtcpPliMessage::RtcpPliMessage(uint32_t ssrc) : remote_ssrc(ssrc) {}
+RtcpPliMessage::RtcpPliMessage() : remote_ssrc(0) {}
+
 RtcpReceiverEventLogMessage::RtcpReceiverEventLogMessage()
     : type(UNKNOWN), packet_id(0u) {}
 RtcpReceiverEventLogMessage::~RtcpReceiverEventLogMessage() {}