Add methods for telling V8 how much memory audio/video is using.

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 c06dd295de9dfe8b111c01aad19ce5a83c13f54b..7b843963f276b9c4877d823dc6a537f465696153 100644
--- a/media/filters/ffmpeg_demuxer.cc
+++ b/media/filters/ffmpeg_demuxer.cc
@@ -917,6 +917,15 @@ void FFmpegDemuxer::AddTextStreams() {
   }
 }
 
+int64_t FFmpegDemuxer::GetMemoryUsage() const {
+  int64_t allocation_size = 0;
+  for (const auto& stream : streams_) {
+    if (stream)
+      allocation_size += stream->MemoryUsage();
+  }
+  return allocation_size;
+}
+
 // Helper for calculating the bitrate of the media based on information stored
 // in |format_context| or failing that the size and duration of the media.
 //