Remove AudioDecoder from the Filter heirarchy.

media/filters/ffmpeg_audio_decoder.h

Index: media/filters/ffmpeg_audio_decoder.h
diff --git a/media/filters/ffmpeg_audio_decoder.h b/media/filters/ffmpeg_audio_decoder.h
index 0cfd456bdbac74faefce34d2ab8ebde6c79bf610..12f50dc1ee68a73d5c7823164cea9a2bdf1a27e7 100644
--- a/media/filters/ffmpeg_audio_decoder.h
+++ b/media/filters/ffmpeg_audio_decoder.h
@@ -8,7 +8,7 @@
 #include <list>
 
 #include "base/message_loop.h"
-#include "media/base/filters.h"
+#include "media/base/audio_decoder.h"
 
 struct AVCodecContext;
 
@@ -21,9 +21,6 @@ class MEDIA_EXPORT FFmpegAudioDecoder : public AudioDecoder {
   explicit FFmpegAudioDecoder(MessageLoop* message_loop);
   virtual ~FFmpegAudioDecoder();
 
-  // Filter implementation.
-  virtual void Flush(const base::Closure& callback) OVERRIDE;
-
   // AudioDecoder implementation.
   virtual void Initialize(DemuxerStream* stream,
                           const PipelineStatusCB& callback,