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.
render() {
          return <a>{this.props.children}</a>;
        }
      }
      ReactTestUtils.renderIntoDocument(<Link><div><Link /></div></Link>);
      expectDev(console.error.calls.count()).toBe(6);
      expectDev(
        normalizeCodeLocInfo(console.error.calls.argsFor(5)[0]),
      ).toContain(
        ReactDOMFeatureFlags.useFiber
          ? '\n    in a (at **)' +
              '\n    in Link (at **)' +
              '\n    in div (at **)' +
              '\n    in a (at **)' +
              '\n    in Link (at **)'
          : 'See Link > a > ... > Link > a.',
      );
    });
    it('should warn about incorrect casing on properties (ssr)', () => {
      spyOn(console, 'error');
      ReactDOMServer.renderToString(
        React.createElement('input', {type: 'text', tabindex: '1'}),
      );
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(console.error.calls.argsFor(0)[0]).toContain('tabIndex');
    });