return(value) {
		            if (!IsReadableStreamAsyncIterator(this)) {
		                return promiseRejectedWith(streamAsyncIteratorBrandCheckException('return'));
		            }
		            return this._asyncIteratorImpl.return(value);
		        }
Tees this readable stream, returning a two-element array containing the two resulting branches as
new {@link ReadableStream} instances.

Teeing a stream will lock it, preventing any other consumer from acquiring a reader.
To cancel the stream, cancel both of the resulting branches; a composite cancellation reason will then be
propagated to the stream's underlying source.

Note that the chunks seen in each branch will be the same object. If the chunks are not immutable,
this could allow interference between the two branches.