[Cast] In Audio/VideoSender, drop frames when too-long a duration is in-flight.

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 b531a069fe46022d5089aab45b79945e8f8c64dc..b5a9dc96a4806e3baff209fdde38f156d7f681ea 100644
--- a/media/cast/sender/frame_sender.cc
+++ b/media/cast/sender/frame_sender.cc
@@ -51,8 +51,7 @@ void FrameSender::SendRtcpReport(bool schedule_future_reports) {
   DCHECK(cast_environment_->CurrentlyOn(CastEnvironment::MAIN));
   const base::TimeTicks now = cast_environment_->Clock()->NowTicks();
   uint32 now_as_rtp_timestamp = 0;
-  if (rtp_timestamp_helper_.GetCurrentTimeAsRtpTimestamp(
-          now, &now_as_rtp_timestamp)) {
+  if (rtp_timestamp_helper_.EstimateRtpTimestamp(now, &now_as_rtp_timestamp)) {
     transport_sender_->SendSenderReport(ssrc_, now, now_as_rtp_timestamp);
   } else {
     // |rtp_timestamp_helper_| should have stored a mapping by this point.
@@ -81,6 +80,9 @@ void FrameSender::SetTargetPlayoutDelay(
                1 + static_cast<int>(target_playout_delay_ *
                                     max_frame_rate_ /
                                     base::TimeDelta::FromSeconds(1)));
+  max_unacked_rtp_delta_ =
+      1 + TimeDeltaToRtpDelta(target_playout_delay_,
+                              rtp_timestamp_helper_.frequency());
   send_target_playout_delay_ = true;
 }