Function factory

test/angular/1.4/angular.js:4430–4434

(name, factoryFn, enforce)

  }

  function factory(name, factoryFn, enforce) {
    return provider(name, {
      $get: enforce !== false ? enforceReturnValue(name, factoryFn) : factoryFn
    });
  }

  function service(name, constructor) {
    return factory(name, ['$injector', function($injector) {