/**
 * A condition for checking the number of opened windows.
 *
 * @example
 * browser.waitUntil(numberOfWindowsToBe(2));
 *
 * @param {!number} expectedNumber The expected url
 * @returns {!function} A condition that returns a promise
 *     representing whether browser's windows length.
 */
export declare function numberOfWindowsToBe(expectedNumber: number): () => Promise<boolean>;