Method define

testing/fake-dom.js:708–714

* Custom Elements V1 API. * @param {string} name * @param {!Function} klass

(name, klass)

   * @param {!Function} klass
   */
  define(name, klass) {
    if (this.elements[name]) {
      throw new Error('custom element already defined: ' + name);
    }
    this.elements[name] = klass.prototype;
    this.count++;
  }
}

export class FakeMutationObserver {