Replaced DCHECKs to use MessageLoop::current() for FFmpegDemuxer and DecoderBase.

media/filters/ffmpeg_demuxer.h

Index: media/filters/ffmpeg_demuxer.h
diff --git a/media/filters/ffmpeg_demuxer.h b/media/filters/ffmpeg_demuxer.h
index 8c4e128d8216efef6fe25c585f38db451ec03ed9..9d68e35823318369a507871a847bab57d3894d00 100644
--- a/media/filters/ffmpeg_demuxer.h
+++ b/media/filters/ffmpeg_demuxer.h
@@ -128,9 +128,6 @@ class FFmpegDemuxer : public Demuxer {
   virtual scoped_refptr<DemuxerStream> GetStream(int stream_id);
 
  private:
-  // Allow FFmpegDemuxerStream to post tasks to our message loop.
-  friend class FFmpegDemuxerStream;
-
   // Only allow a factory to create this class.
   friend class FilterFactoryImpl0<FFmpegDemuxer>;
   FFmpegDemuxer();
@@ -181,9 +178,6 @@ class FFmpegDemuxer : public Demuxer {
   StreamVector streams_;
   StreamVector packet_streams_;
 
-  // Used for debugging.
-  PlatformThreadId thread_id_;
-
   DISALLOW_COPY_AND_ASSIGN(FFmpegDemuxer);
 };