Method fork

packages/zone.js/lib/zone-impl.ts:868–871

(zoneSpec: ZoneSpec)

    }

    public fork(zoneSpec: ZoneSpec): AmbientZone {
      if (!zoneSpec) throw new Error('ZoneSpec required!');
      return this._zoneDelegate.fork(this, zoneSpec);
    }

    public wrap<T extends Function>(callback: T, source: string): T {
      if (typeof callback !== 'function') {