Add Cast PLI support on sender side.

media/cast/net/rtcp/rtcp_defines.h

Index: media/cast/net/rtcp/rtcp_defines.h
diff --git a/media/cast/net/rtcp/rtcp_defines.h b/media/cast/net/rtcp/rtcp_defines.h
index 69a81bf8c94b9e7e8384abd941b96fc28d47006d..a2be224e24d1e1a9f5e35cd54e506abce5bb4b8c 100644
--- a/media/cast/net/rtcp/rtcp_defines.h
+++ b/media/cast/net/rtcp/rtcp_defines.h
@@ -51,6 +51,7 @@ struct RtcpCastMessage {
   uint32_t media_ssrc;
   uint32_t ack_frame_id;
   uint16_t target_delay_ms;
+  bool picture_loss_indicator;

[miu, 2016/02/26 23:36:06]

This isn't part of the Cast Feedback message.  I'd suggest removing this and
instead and adding some simple plumbing in the receiver code (see comment in
receiver_rtcp_session.cc).

[xjz, 2016/02/27 05:53:32]

Done.

   MissingFramesAndPacketsMap missing_frames_and_packets;
 };
 
@@ -116,6 +117,7 @@ typedef base::Callback<void(const RtcpCastMessage&)> RtcpCastMessageCallback;
 typedef base::Callback<void(base::TimeDelta)> RtcpRttCallback;
 typedef
 base::Callback<void(const RtcpReceiverLogMessage&)> RtcpLogMessageCallback;
+typedef base::Callback<void()> RtcpPliCallback;
 
 // TODO(hubbe): Document members of this struct.
 struct RtpReceiverStatistics {