[Cast] Track audio queued in encoder; account for it in ShouldDropNextFrame().

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 26609c16aa268ce24c2bfbc527262aa225687020..f1783166d840cab406e8602193eb2e1f4d9bbced 100644
--- a/media/cast/sender/video_sender.h
+++ b/media/cast/sender/video_sender.h
@@ -57,14 +57,22 @@ class VideoSender : public FrameSender,
                            const base::TimeTicks& capture_time);
 
  protected:
+  virtual int GetNumberOfFramesInEncoder() const OVERRIDE;
   virtual void OnAck(uint32 frame_id) OVERRIDE;
 
  private:
+  // Called by the |video_encoder_| with the next EncodedFrame to send.
+  void OnEncodedVideoFrame(int encoder_bitrate,
+                           scoped_ptr<EncodedFrame> encoded_frame);
+
   // Encodes media::VideoFrame images into EncodedFrames.  Per configuration,
   // this will point to either the internal software-based encoder or a proxy to
   // a hardware-based encoder.
   scoped_ptr<VideoEncoder> video_encoder_;
 
+  // The number of frames queued for encoding, but not yet sent.
+  int frames_in_encoder_;
+
   // Remember what we set the bitrate to before, no need to set it again if
   // we get the same value.
   uint32 last_bitrate_;