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

media/blink/buffered_data_source.cc

Index: media/blink/buffered_data_source.cc
diff --git a/media/blink/buffered_data_source.cc b/media/blink/buffered_data_source.cc
index 0aa85613c4907079308723957840fff36c3a1eb3..d417c2c183af677e558009154a0fcece7677f2f5 100644
--- a/media/blink/buffered_data_source.cc
+++ b/media/blink/buffered_data_source.cc
@@ -237,6 +237,11 @@ void BufferedDataSource::OnBufferingHaveEnough() {
     loader_->CancelUponDeferral();
 }
 
+int64_t BufferedDataSource::GetMemoryUsage() const {
+  DCHECK(render_task_runner_->BelongsToCurrentThread());
+  return loader_ ? loader_->GetMemoryUsage() : 0;
+}
+
 void BufferedDataSource::Read(
     int64 position, int size, uint8* data,
     const DataSource::ReadCB& read_cb) {