Add Cast PLI support on sender side.

media/cast/net/rtcp/rtcp_builder.h

Index: media/cast/net/rtcp/rtcp_builder.h
diff --git a/media/cast/net/rtcp/rtcp_builder.h b/media/cast/net/rtcp/rtcp_builder.h
index c98534348957e5376aca843e49dcea6b9d1cfe11..92407cafce65fdbd92bc1cd3fb6c87187d2542b7 100644
--- a/media/cast/net/rtcp/rtcp_builder.h
+++ b/media/cast/net/rtcp/rtcp_builder.h
@@ -31,6 +31,7 @@ class RtcpBuilder {
       const RtcpReportBlock* report_block,
       const RtcpReceiverReferenceTimeReport* rrtr,
       const RtcpCastMessage* cast_message,
+      const RtcpPliMessage* pli_message,
       const ReceiverRtcpEventSubscriber::RtcpEvents* rtcp_events,
       base::TimeDelta target_delay);
 
@@ -48,6 +49,7 @@ class RtcpBuilder {
   void AddDlrrRb(const RtcpDlrrReportBlock& dlrr);
   void AddReceiverLog(
       const ReceiverRtcpEventSubscriber::RtcpEvents& rtcp_events);
+  void AddPli(const RtcpPliMessage* pli_message);
 
   bool GetRtcpReceiverLogMessage(
       const ReceiverRtcpEventSubscriber::RtcpEvents& rtcp_events,