A client of ReadableByteStreamController may use these functions directly to bypass state check.
function ReadableByteStreamControllerClose(controller) {
  const stream = controller._controlledReadableStream;

  assert(controller._closeRequested === false);
  assert(stream._state === 'readable');

  if (controller._totalQueuedBytes > 0) {
    controller._closeRequested = true;

    return;
  }

  if (controller._pendingPullIntos.length > 0) {
    const firstPendingPullInto = controller._pendingPullIntos[0];
    if (firstPendingPullInto.bytesFilled > 0) {
      const e = new TypeError('Insufficient bytes to fill elements in the given buffer');
      ReadableByteStreamControllerError(controller, e);

      throw e;
    }
  }

  ReadableStreamClose(stream);
}