Function create_readable_stream 

pub(crate) fn create_readable_stream(
    cx: &mut JSContext,
    global: &GlobalScope,
    underlying_source_type: UnderlyingSourceType,
    queuing_strategy: Option<Rc<QueuingStrategySize<DomTypeHolder>>>,
    high_water_mark: Option<f64>,
) -> DomRoot<ReadableStream>

https://streams.spec.whatwg.org/#create-readable-stream