Add Cast PLI support on sender side.

media/cast/sender/frame_sender.cc

Index: media/cast/sender/frame_sender.cc
diff --git a/media/cast/sender/frame_sender.cc b/media/cast/sender/frame_sender.cc
index 8ddfdb7e39c2e898236b91ad3177a4c785edea5a..31eff5a824878a2ff60176d7ce3dc6cd9af0cfee 100644
--- a/media/cast/sender/frame_sender.cc
+++ b/media/cast/sender/frame_sender.cc
@@ -59,6 +59,7 @@ FrameSender::FrameSender(scoped_refptr<CastEnvironment> cast_environment,
       latest_acked_frame_id_(0),
       duplicate_ack_counter_(0),
       congestion_control_(congestion_control),
+      picture_lost_at_receiver_(false),
       rtp_timebase_(rtp_timebase),
       is_audio_(is_audio),
       weak_factory_(this) {
@@ -219,8 +220,20 @@ void FrameSender::SendEncodedFrame(
           << last_sent_frame_id_ << ", latest_acked=" << latest_acked_frame_id_;
 
   const uint32_t frame_id = encoded_frame->frame_id;
-
   const bool is_first_frame_to_be_sent = last_send_time_.is_null();
+
+  if (picture_lost_at_receiver_ &&
+      (encoded_frame->dependency == EncodedFrame::KEY)) {
+    picture_lost_at_receiver_ = false;
+    DCHECK(frame_id > latest_acked_frame_id_);
+    // Cancel sending remaining frames.
+    std::vector<uint32_t> cancel_sending_frames;
+    for (uint32_t id = latest_acked_frame_id_ + 1; id < frame_id; ++id) {
+      cancel_sending_frames.push_back(id);
+    }
+    transport_sender_->CancelSendingFrames(ssrc_, cancel_sending_frames);
+  }
+
   last_send_time_ = cast_environment_->Clock()->NowTicks();
   last_sent_frame_id_ = frame_id;
   // If this is the first frame about to be sent, fake the value of
@@ -381,6 +394,10 @@ void FrameSender::OnReceivedCastFeedback(const RtcpCastMessage& cast_feedback) {
   }
 }
 
+void FrameSender::OnReceivedPli() {
+  picture_lost_at_receiver_ = true;
+}
+
 bool FrameSender::ShouldDropNextFrame(base::TimeDelta frame_duration) const {
   // Check that accepting the next frame won't cause more frames to become
   // in-flight than the system's design limit.