constructor() {
    /**
     * The desired size to fill the controlled stream's internal queue.
     * It can be negative if the queue is full.
     * https://streams.spec.whatwg.org/#rs-default-controller-desired-size
     * @type {?number}
     */
    this.desiredSize;
  }
The controller for a ReadableStream. Adds cancellation and backpressure.
@template T
@interface
@extends {liteTypes.ReadableStreamDefaultController<T>}