RouterOutlet(ViewContainerRef _viewContainerRef, ComponentResolver _loader, Router _parentRouter, @ String nameAttr)

Source 

RouterOutlet(this._viewContainerRef, this._loader, this._parentRouter,
    @Attribute("name") String nameAttr) {
  if (nameAttr != null) {
    this.name = nameAttr;
    this._parentRouter.registerAuxOutlet(this);
  } else {
    this._parentRouter.registerPrimaryOutlet(this);
  }
}