Fix ChunkDemuxer seek deadlock

media/base/demuxer_stream.h

-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
 #ifndef MEDIA_BASE_DEMUXER_STREAM_H_
 #define MEDIA_BASE_DEMUXER_STREAM_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "media/base/media_export.h"
 
 namespace media {
 
 class AudioDecoderConfig;
 class Buffer;
 class VideoDecoderConfig;
 
 class MEDIA_EXPORT DemuxerStream
     : public base::RefCountedThreadSafe<DemuxerStream> {
  public:
   enum Type {
     UNKNOWN,
     AUDIO,
     VIDEO,
     NUM_TYPES,  // Always keep this entry as the last one!
   };
 
   // Request a buffer to returned via the provided callback.
   //
-  // Buffers will be non-NULL yet may be end of stream buffers.
+  // Non-NULL buffer pointers will contain media data or signal the end of the
+  // stream. A NULL pointer indicates an aborted Read(). This can happen if the
+  // DemuxerStream gets flushed and doesn't have any more data to return.
   typedef base::Callback<void(const scoped_refptr<Buffer>&)> ReadCallback;
   virtual void Read(const ReadCallback& read_callback) = 0;
 
   // Returns the audio decoder configuration. It is an error to call this method
   // if type() != AUDIO.
   virtual const AudioDecoderConfig& audio_decoder_config() = 0;
 
   // Returns the video decoder configuration. It is an error to call this method
   // if type() != VIDEO.
   virtual const VideoDecoderConfig& video_decoder_config() = 0;
 
   // Returns the type of stream.
   virtual Type type() = 0;
 
   virtual void EnableBitstreamConverter() = 0;
 
  protected:
   friend class base::RefCountedThreadSafe<DemuxerStream>;
   virtual ~DemuxerStream();
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_DEMUXER_STREAM_H_