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

media/cast/sender/audio_sender.cc

Index: media/cast/sender/audio_sender.cc
diff --git a/media/cast/sender/audio_sender.cc b/media/cast/sender/audio_sender.cc
index 4bf93b30cd615ce90f4b061070fcb2955283af8e..2d1790481e8fa752d59eb1469b261427c668123f 100644
--- a/media/cast/sender/audio_sender.cc
+++ b/media/cast/sender/audio_sender.cc
@@ -90,7 +90,7 @@ void AudioSender::InsertAudio(scoped_ptr<AudioBus> audio_bus,
   }
   DCHECK(audio_encoder_.get()) << "Invalid internal state";
 
-  if (AreTooManyFramesInFlight()) {
+  if (ShouldDropNextFrame(recorded_time)) {
     VLOG(1) << "Dropping frame due to too many frames currently in-flight.";
     return;
   }
@@ -112,6 +112,8 @@ void AudioSender::SendEncodedAudioFrame(
   // Also, schedule the periodic frame re-send checks.
   if (is_first_frame_to_be_sent) {
     latest_acked_frame_id_ = frame_id - 1;
+    frame_id_to_rtp_timestamp_[latest_acked_frame_id_ & 0xff] =
+        encoded_frame->rtp_timestamp;
     ScheduleNextResendCheck();
   }
 
@@ -244,17 +246,32 @@ void AudioSender::OnReceivedCastFeedback(const RtcpCastMessage& cast_feedback) {
   }
 }
 
-bool AudioSender::AreTooManyFramesInFlight() const {
+bool AudioSender::ShouldDropNextFrame(base::TimeTicks capture_time) const {
   DCHECK(cast_environment_->CurrentlyOn(CastEnvironment::MAIN));
   int frames_in_flight = 0;
+  int32 rtp_duration_in_flight = 0;
   if (!last_send_time_.is_null()) {
-    frames_in_flight +=
+    frames_in_flight =
         static_cast<int32>(last_sent_frame_id_ - latest_acked_frame_id_);
+    uint32 estimated_rtp_timestamp;
+    if (frames_in_flight > 0 &&
+        rtp_timestamp_helper_.EstimateRtpTimestamp(capture_time,
+                                                   &estimated_rtp_timestamp)) {
+      const uint32 oldest_unacked_frame_id = latest_acked_frame_id_ + 1;
+      rtp_duration_in_flight = static_cast<int32>(
+          estimated_rtp_timestamp -
+              frame_id_to_rtp_timestamp_[oldest_unacked_frame_id & 0xff]);
+    }
   }
   VLOG(2) << frames_in_flight
           << " frames in flight; last sent: " << last_sent_frame_id_
-          << " latest acked: " << latest_acked_frame_id_;
-  return frames_in_flight >= max_unacked_frames_;
+          << "; latest acked: " << latest_acked_frame_id_
+          << "; duration in flight: "
+          << (max_unacked_rtp_delta_ > 0 ?
+                  100 * rtp_duration_in_flight / max_unacked_rtp_delta_ :
+                  kint32max) << "%";
+  return frames_in_flight >= max_unacked_frames_ ||
+      rtp_duration_in_flight >= max_unacked_rtp_delta_;
 }
 
 void AudioSender::ResendForKickstart() {