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 3272f741de4a691ee6562d962dcc638008f91ec3..db1c170b24b94eed180cc74ae4255ed5c52264a9 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.