Add support for cancellation of demuxer reads.

media/base/data_source.h

 // 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_DATA_SOURCE_H_
 #define MEDIA_BASE_DATA_SOURCE_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "media/base/media_export.h"
 
 namespace media {
 
 class MEDIA_EXPORT DataSource {
  public:
   typedef base::Callback<void(int64_t, int64_t)> StatusCallback;
   typedef base::Callback<void(int)> ReadCB;
 
-  enum { kReadError = -1 };
+  enum { kReadError = -1, kAborted = -2 };
 
   DataSource();
   virtual ~DataSource();
 
   // Reads |size| bytes from |position| into |data|. And when the read is done
   // or failed, |read_cb| is called with the number of bytes read or
   // kReadError in case of error.
   virtual void Read(int64_t position,
                     int size,
                     uint8_t* data,
                     const DataSource::ReadCB& read_cb) = 0;
 
   // Stops the DataSource. Once this is called all future Read() calls will
   // return an error.
   virtual void Stop() = 0;
 
+  // Similar to Stop(), but only aborts current reads and not future reads.
+  virtual void Abort() = 0;
+
   // Returns true and the file size, false if the file size could not be
   // retrieved.
   virtual bool GetSize(int64_t* size_out) = 0;
 
   // Returns true if we are performing streaming. In this case seeking is
   // not possible.
   virtual bool IsStreaming() = 0;
 
   // Notify the DataSource of the bitrate of the media.
   // Values of |bitrate| <= 0 are invalid and should be ignored.
   virtual void SetBitrate(int bitrate) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DataSource);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_DATA_SOURCE_H_