static notAbortable(promise) {
    return new shaka.util.AbortableOperation(
        promise,
        // abort() here will return a Promise which is resolved when the input
        // promise either resolves or fails.
        () => promise.catch(() => {}));
  }
@param {!Promise<U>} promise
@return {!shaka.util.AbortableOperation.<U>} An operation which cannot be
  aborted.  It will be completed when the given Promise is resolved, or
  will be failed when the given Promise is rejected.
@template U
@export