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

media/blink/buffered_data_source.h

Index: media/blink/buffered_data_source.h
diff --git a/media/blink/buffered_data_source.h b/media/blink/buffered_data_source.h
index fd85b7cc524e3e79395313e3e59ed33015bcf250..9762050af4d4c0593d8dbaa369957d613cb520c2 100644
--- a/media/blink/buffered_data_source.h
+++ b/media/blink/buffered_data_source.h
@@ -113,6 +113,9 @@ class MEDIA_EXPORT BufferedDataSource : public DataSource {
   // If already deferred, connections will be immediately closed.
   void OnBufferingHaveEnough();
 
+  // Returns an estimate of the number of bytes held by the data source.
+  int64_t GetMemoryUsage() const;
+
   // DataSource implementation.
   // Called from demuxer thread.
   void Stop() override;