recordRequestSize method
Records the request body's size, for a transport that learns it only once the request has been dispatched.
dart:io is one: its contentLength is set by the caller after the request
object exists. Without this the app-wide path would be the one integration that
never reports http.request_body.size.
Implementation
void recordRequestSize(int size) =>
_span.setInt('http.request_body.size', size);