get closed() {
		            if (!IsReadableStreamBYOBReader(this)) {
		                return promiseRejectedWith(byobReaderBrandCheckException('closed'));
		            }
		            return this._closedPromise;
		        }
The Blob interface's slice() method creates and returns a
new Blob object which contains data from a subset of the
blob on which it's called.

@param {number} [start]
@param {number} [end]
@param {string} [type]