Add Cast PLI support on sender side.

media/cast/receiver/frame_receiver.cc

Index: media/cast/receiver/frame_receiver.cc
diff --git a/media/cast/receiver/frame_receiver.cc b/media/cast/receiver/frame_receiver.cc
index 7236135ae5460d5699944266a392bc360dfbfa23..d212dc735f02035878438ea0f9467b3aabe8296e 100644
--- a/media/cast/receiver/frame_receiver.cc
+++ b/media/cast/receiver/frame_receiver.cc
@@ -197,7 +197,7 @@ void FrameReceiver::CastFeedback(const RtcpCastMessage& cast_message) {
   event_subscriber_.GetRtcpEventsWithRedundancy(&rtcp_events);
   transport_->SendRtcpFromRtpReceiver(
       rtcp_.local_ssrc(), rtcp_.remote_ssrc(), CreateRtcpTimeData(now),
-      &cast_message, target_playout_delay_, &rtcp_events, NULL);
+      &cast_message, nullptr, target_playout_delay_, &rtcp_events, nullptr);
 }
 
 void FrameReceiver::EmitAvailableEncodedFrames() {
@@ -350,8 +350,8 @@ void FrameReceiver::SendNextRtcpReport() {
   const base::TimeTicks now = cast_environment_->Clock()->NowTicks();
   RtpReceiverStatistics stats = stats_.GetStatistics();
   transport_->SendRtcpFromRtpReceiver(rtcp_.local_ssrc(), rtcp_.remote_ssrc(),
-                                      CreateRtcpTimeData(now), NULL,
-                                      base::TimeDelta(), NULL, &stats);
+                                      CreateRtcpTimeData(now), nullptr, nullptr,
+                                      base::TimeDelta(), nullptr, &stats);
   ScheduleNextRtcpReport();
 }