Two issues:
1. There was a typo, the first `gen` should have been `genFn`.
2. And the last `toString` result should be `'[object Generator]'`,
because `Object.getPrototypeOf(gen) == genFn.prototype`. And the
`@@toStringTag` property of `genFn.prototype` is inherited from
`Generator.prototype[@@toStringTag]`.
That also means the "iterator-helpers" flag isn't needed for this test.
f0c16faee2