static getManifest_(uri, request) {
    /** @type {shaka.extern.Response} */
    const response = {
      uri: uri,
      originalUri: uri,
      data: new ArrayBuffer(0),
      headers: {'content-type': 'application/x-offline-manifest'},
      originalRequest: request,
    };

    return shaka.util.AbortableOperation.completed(response);
  }
@param {string} uri
@param {shaka.extern.Request} request
@return {!shaka.extern.IAbortableOperation.<shaka.extern.Response>}
@private