Convert Filter::Seek() to use new callback system.

media/filters/ffmpeg_demuxer.h

Index: media/filters/ffmpeg_demuxer.h
diff --git a/media/filters/ffmpeg_demuxer.h b/media/filters/ffmpeg_demuxer.h
index 3fe2cf1aeea8ace0e200fa38f6a4c60fd3e557b4..d96622ca398da151f031d5340d967563395a3ca4 100644
--- a/media/filters/ffmpeg_demuxer.h
+++ b/media/filters/ffmpeg_demuxer.h
@@ -142,7 +142,7 @@ class FFmpegDemuxer : public Demuxer,
 
   // Filter implementation.
   virtual void Stop(FilterCallback* callback);
-  virtual void Seek(base::TimeDelta time, FilterCallback* callback);
+  virtual void Seek(base::TimeDelta time, const FilterStatusCB& cb);
   virtual void OnAudioRendererDisabled();
   virtual void set_host(FilterHost* filter_host);
   virtual void SetPlaybackRate(float playback_rate);
@@ -171,7 +171,7 @@ class FFmpegDemuxer : public Demuxer,
       DataSource* data_source, PipelineStatusCallback* callback);
 
   // Carries out a seek on the demuxer thread.
-  void SeekTask(base::TimeDelta time, FilterCallback* callback);
+  void SeekTask(base::TimeDelta time, const FilterStatusCB& cb);
 
   // Carries out demuxing and satisfying stream reads on the demuxer thread.
   void DemuxTask();