Adding ChunkDemuxer implementation.

media/filters/ffmpeg_demuxer.cc

Index: media/filters/ffmpeg_demuxer.cc
diff --git a/media/filters/ffmpeg_demuxer.cc b/media/filters/ffmpeg_demuxer.cc
index 0ee711fd546ce61954585effb15be903ae25d7aa..58082b10e80f9a3957ed46fe977ea40b61866f84 100644
--- a/media/filters/ffmpeg_demuxer.cc
+++ b/media/filters/ffmpeg_demuxer.cc
@@ -280,25 +280,7 @@ FFmpegDemuxer::~FFmpegDemuxer() {
   if (!format_context_)
     return;
 
-  // Iterate each stream and destroy each one of them.
-  int streams = format_context_->nb_streams;
-  for (int i = 0; i < streams; ++i) {
-    AVStream* stream = format_context_->streams[i];
-
-    // The conditions for calling avcodec_close():
-    // 1. AVStream is alive.
-    // 2. AVCodecContext in AVStream is alive.
-    // 3. AVCodec in AVCodecContext is alive.
-    // Notice that closing a codec context without prior avcodec_open() will
-    // result in a crash in FFmpeg.
-    if (stream && stream->codec && stream->codec->codec) {
-      stream->discard = AVDISCARD_ALL;
-      avcodec_close(stream->codec);
-    }
-  }
-
-  // Then finally cleanup the format context.
-  av_close_input_file(format_context_);
+  DestroyAVFormatContext(format_context_);
   format_context_ = NULL;
 }