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.
return props.children;
      }
      function Owner() {
        
        
        
        return (
          <Parent>
            <input dangerouslySetInnerHTML={{__html: 'content'}} />
          </Parent>
        );
      }
      expect(function() {
        ReactDOM.render(<Owner />, container);
      }).toThrowError('\n\nThis DOM node was rendered by `Owner`.');
    });
    it('should emit a warning once for a named custom component using shady DOM', () => {
      spyOn(console, 'error');
      var defaultCreateElement = document.createElement.bind(document);
      try {
        document.createElement = element => {
          var container = defaultCreateElement(element);
          container.shadyRoot = {};
          return container;
        };
        class ShadyComponent extends React.Component {