Add the "virtual" keyword on method overrides that are missing it.

media/filters/ffmpeg_demuxer.h

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Implements the Demuxer interface using FFmpeg's libavformat.  At this time
 // will support demuxing any audio/video format thrown at it.  The streams
 // output mime types audio/x-ffmpeg and video/x-ffmpeg and include an integer
 // key FFmpegCodecID which contains the CodecID enumeration value.  The CodecIDs
 // can be used to create and initialize the corresponding FFmpeg decoder.
 //
@@ skipping 57 matching lines @@
   // Empties the queues and ignores any additional calls to Read().
   virtual void Stop();
 
   // Returns the duration of this stream.
   virtual base::TimeDelta duration() { return duration_; }
 
   // DemuxerStream implementation.
   virtual const MediaFormat& media_format();
   virtual void Read(Callback1<Buffer*>::Type* read_callback);
   // Bitstream converter to convert input packet.
-  void EnableBitstreamConverter();
+  virtual void EnableBitstreamConverter();
 
   // AVStreamProvider implementation.
   virtual AVStream* GetAVStream() { return stream_; }
 
 
 
  protected:
   virtual void* QueryInterface(const char* interface_id);
 
  private:
@@ skipping 131 matching lines @@
 
   size_t last_read_bytes_;
   int64 read_position_;
 
   DISALLOW_COPY_AND_ASSIGN(FFmpegDemuxer);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_FFMPEG_DEMUXER_H_