Add Cast PLI support on sender side.

media/cast/net/cast_transport_sender.h

Index: media/cast/net/cast_transport_sender.h
diff --git a/media/cast/net/cast_transport_sender.h b/media/cast/net/cast_transport_sender.h
index 993e74f0d4845419a47259a95970f4e891fb4c1c..cad68d4a3fbbb41f77bd866261505acdd294c7f1 100644
--- a/media/cast/net/cast_transport_sender.h
+++ b/media/cast/net/cast_transport_sender.h
@@ -95,10 +95,12 @@ class CastTransportSender : public base::NonThreadSafe {
   // is called.
   virtual void InitializeAudio(const CastTransportRtpConfig& config,
                                const RtcpCastMessageCallback& cast_message_cb,
-                               const RtcpRttCallback& rtt_cb) = 0;
+                               const RtcpRttCallback& rtt_cb,
+                               const RtcpPliCallback& pli_cb) = 0;
   virtual void InitializeVideo(const CastTransportRtpConfig& config,
                                const RtcpCastMessageCallback& cast_message_cb,
-                               const RtcpRttCallback& rtt_cb) = 0;
+                               const RtcpRttCallback& rtt_cb,
+                               const RtcpPliCallback& pli_cb) = 0;
 
   // Encrypt, packetize and transmit |frame|. |ssrc| must refer to a
   // a channel already established with InitializeAudio / InitializeVideo.
@@ -145,6 +147,7 @@ class CastTransportSender : public base::NonThreadSafe {
 
   virtual void AddCastFeedback(const RtcpCastMessage& cast_message,
                                base::TimeDelta target_delay) = 0;
+  virtual void AddPli(const RtcpPliMessage& pli_message) = 0;
   virtual void AddRtcpEvents(
       const ReceiverRtcpEventSubscriber::RtcpEvents& rtcp_events) = 0;
   virtual void AddRtpReceiverReport(