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

media/cast/sender/video_sender.h

Index: media/cast/sender/video_sender.h
diff --git a/media/cast/sender/video_sender.h b/media/cast/sender/video_sender.h
index 9b6e62e22791c39f66213beb40b233fa08bf9612..ad0a6d88937cc81219f5853e7bf0a3d262ffc0ec 100644
--- a/media/cast/sender/video_sender.h
+++ b/media/cast/sender/video_sender.h
@@ -54,7 +54,6 @@ class VideoSender : public FrameSender,
                            const base::TimeTicks& capture_time);
 
  protected:
-  virtual int GetNumberOfFramesInEncoder() const OVERRIDE;
   virtual void OnAck(uint32 frame_id) OVERRIDE;
 
  private:
@@ -75,6 +74,12 @@ class VideoSender : public FrameSender,
   // The number of frames queued for encoding, but not yet sent.
   int frames_in_encoder_;
 
+  // The duration of video queued for encoding, but not yet sent.
+  base::TimeDelta duration_in_encoder_;
+
+  // The timestamp of the frame that was last enqueued in |video_encoder_|.
+  base::TimeTicks last_enqueued_frame_reference_time_;
+
   // Remember what we set the bitrate to before, no need to set it again if
   // we get the same value.
   uint32 last_bitrate_;