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.
<div>
          <div key="one">
            <div key="A">A</div><div key="B">B</div>
          </div>
          <div key="two">
            <div key="C">C</div><div key="D">D</div>
          </div>
        </div>,
        container,
      );
      
      ReactDOM.render(
        <div>
          <div key="one">
            <div key="B">B</div><div key="A">A</div>
          </div>
          <div key="two">
            <div key="D">D</div><div key="C">C</div>
          </div>
        </div>,
        container,
      );
      expect(container.textContent).toBe('BADC');
    });
  });
  describe('createOpenTagMarkup', () => {
    function quoteRegexp(str) {
      return (str + '').replace(/([.?*+\^$\[\]\\(){}|-])/g, '\\$1');
    }
    function toHaveAttribute(actual, expected) {