Enable video in linux build and remove unneeded ifdefs to guard windows.

media/filters/ffmpeg_demuxer.h

 // Copyright (c) 2009 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 17 matching lines @@
 #include "media/base/factory.h"
 #include "media/base/filters.h"
 #include "media/base/media_format.h"
 
 // FFmpeg forward declarations.
 struct AVCodecContext;
 struct AVBitStreamFilterContext;
 struct AVFormatContext;
 struct AVPacket;
 struct AVStream;
-enum CodecID;
 
 namespace media {
 
 class FFmpegDemuxer;
 
 // Forward declaration for scoped_ptr_malloc.
 class ScopedPtrAVFree;
 
 class FFmpegDemuxerStream : public DemuxerStream {
  public:
@@ skipping 114 matching lines @@
 
   // Thread handle.
   base::Thread thread_;
 
   DISALLOW_COPY_AND_ASSIGN(FFmpegDemuxer);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_FFMPEG_DEMUXER_H_