We used to throw if event listener is not a function in Stack:

```js
ReactDOM.render(
  <h1 onClick={{}}>Hello World!</h1>,
  document.getElementById('container')
);
```

<img width="565" alt="screen shot 2017-08-08 at 3 41 08 pm" src="https://user-images.githubusercontent.com/810438/29077502-2646412e-7c50-11e7-8c99-3b7f6c0a2589.png">

Fiber silently ignores this.

I think we should throw. This would let us add support for objects (e.g. for passive listener configuration) if we want to in a minor rather than a major.
it('should throw when an attack vector is used', () => {
      var hackzor = React.createElement('div><img /><div');
      expect(() => ReactTestUtils.renderIntoDocument(hackzor)).toThrow();
    });
  });
  describe('nesting validation', () => {
    it('warns on invalid nesting', () => {
      spyOn(console, 'error');
      ReactTestUtils.renderIntoDocument(<div><tr /><tr /></div>);
      var addendum = ReactDOMFeatureFlags.useFiber
        ? '\n    in tr (at **)' + '\n    in div (at **)'
        : ' See div > tr.';
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(normalizeCodeLocInfo(console.error.calls.argsFor(0)[0])).toBe(
        'Warning: validateDOMNesting(...): <tr> cannot appear as a child of ' +
          '<div>.' +
          addendum,
      );
    });
    it('warns on invalid nesting at root', () => {
      spyOn(console, 'error');
      var p = document.createElement('p');
      ReactDOM.render(<span><p /></span>, p);
      var addendum = ReactDOMFeatureFlags.useFiber
        ? 
          '\n    in p (at **)' + '\n    in span (at **)'
        : ' See p > ... > p.';
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(normalizeCodeLocInfo(console.error.calls.argsFor(0)[0])).toBe(
        'Warning: validateDOMNesting(...): <p> cannot appear as a descendant ' +