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

media/blink/buffered_resource_loader.cc

Index: media/blink/buffered_resource_loader.cc
diff --git a/media/blink/buffered_resource_loader.cc b/media/blink/buffered_resource_loader.cc
index 8e875cc87cc842c003c137e46d2967021d2fca36..9abce3fd97d98595e1f81606825844ee41d2db15 100644
--- a/media/blink/buffered_resource_loader.cc
+++ b/media/blink/buffered_resource_loader.cc
@@ -765,6 +765,10 @@ void BufferedResourceLoader::CancelUponDeferral() {
     active_loader_.reset();
 }
 
+int64_t BufferedResourceLoader::GetMemoryUsage() const {
+  return buffer_.forward_bytes() + buffer_.backward_bytes();
+}
+
 bool BufferedResourceLoader::VerifyPartialResponse(
     const WebURLResponse& response) {
   int64 first_byte_position, last_byte_position, instance_size;