[Cast] Limit frames in flight by duration, and not by number of frames.

media/cast/net/rtp/rtp_sender.h

Index: media/cast/net/rtp/rtp_sender.h
diff --git a/media/cast/net/rtp/rtp_sender.h b/media/cast/net/rtp/rtp_sender.h
index 2875114aa34353c5db583eee7160450c65d3e276..a2a5c3871d28924c2ad3d20d8d27e72e440429c5 100644
--- a/media/cast/net/rtp/rtp_sender.h
+++ b/media/cast/net/rtp/rtp_sender.h
@@ -71,8 +71,8 @@ class RtpSender {
 
   base::TickClock* clock_;  // Not owned by this class.
   RtpPacketizerConfig config_;
+  PacketStorage storage_;
   scoped_ptr<RtpPacketizer> packetizer_;
-  scoped_ptr<PacketStorage> storage_;
   PacedSender* const transport_;
   scoped_refptr<base::SingleThreadTaskRunner> transport_task_runner_;