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

media/cast/sender/video_sender.cc

Index: media/cast/sender/video_sender.cc
diff --git a/media/cast/sender/video_sender.cc b/media/cast/sender/video_sender.cc
index f0e3a1440c6c32dc3d59cc7344ee49cf68c6d330..4cd71bd46ce446b11c4087e5cbf4192ec0ecc82f 100644
--- a/media/cast/sender/video_sender.cc
+++ b/media/cast/sender/video_sender.cc
@@ -126,7 +126,7 @@ void VideoSender::InsertRawVideoFrame(
       "timestamp", capture_time.ToInternalValue(),
       "rtp_timestamp", rtp_timestamp);
 
-  if (AreTooManyFramesInFlight()) {
+  if (ShouldDropNextFrame(capture_time)) {
     VLOG(1) << "Dropping frame due to too many frames currently in-flight.";
     return;
   }
@@ -174,6 +174,8 @@ void VideoSender::SendEncodedVideoFrame(
   // 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();
   }
 
@@ -338,18 +340,35 @@ void VideoSender::OnReceivedCastFeedback(const RtcpCastMessage& cast_feedback) {
   }
 }
 
-bool VideoSender::AreTooManyFramesInFlight() const {
+bool VideoSender::ShouldDropNextFrame(base::TimeTicks capture_time) const {
   DCHECK(cast_environment_->CurrentlyOn(CastEnvironment::MAIN));
-  int frames_in_flight = frames_in_encoder_;
+  int frames_in_flight = 0;
+  base::TimeDelta duration_in_flight;
   if (!last_send_time_.is_null()) {
-    frames_in_flight +=
+    frames_in_flight =
         static_cast<int32>(last_sent_frame_id_ - latest_acked_frame_id_);
+    if (frames_in_flight > 0) {
+      const uint32 oldest_unacked_frame_id = latest_acked_frame_id_ + 1;
+      base::TimeTicks oldest_unacked_capture_time;
+      if (rtp_timestamp_helper_.EstimateTimeTicks(
+              frame_id_to_rtp_timestamp_[oldest_unacked_frame_id & 0xff],
+              &oldest_unacked_capture_time)) {
+        duration_in_flight = capture_time - oldest_unacked_capture_time;
+      }
+    }
   }
+  frames_in_flight += frames_in_encoder_;
   VLOG(2) << frames_in_flight
           << " frames in flight; last sent: " << last_sent_frame_id_
-          << " latest acked: " << latest_acked_frame_id_
-          << " frames in encoder: " << frames_in_encoder_;
-  return frames_in_flight >= max_unacked_frames_;
+          << "; latest acked: " << latest_acked_frame_id_
+          << "; frames in encoder: " << frames_in_encoder_
+          << "; duration in flight: "
+          << duration_in_flight.InMicroseconds() << " usec ("
+          << (target_playout_delay_ > base::TimeDelta() ?
+                  100 * duration_in_flight / target_playout_delay_ :
+                  kint64max) << "%)";
+  return frames_in_flight >= max_unacked_frames_ ||
+      duration_in_flight >= target_playout_delay_;
 }
 
 void VideoSender::ResendForKickstart() {