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.
ReactDOM.render(<div className={'bar'} />, container);
      expect(container.firstChild.className).toEqual('bar');
      ReactDOM.render(<div className={null} />, container);
      expect(container.firstChild.className).toEqual('');
    });
    it('should gracefully handle various style value types', () => {
      var container = document.createElement('div');
      ReactDOM.render(<div style={{}} />, container);
      var stubStyle = container.firstChild.style;
      
      var setup = {display: 'block', left: '1px', top: 2, fontFamily: 'Arial'};
      ReactDOM.render(<div style={setup} />, container);
      expect(stubStyle.display).toEqual('block');
      expect(stubStyle.left).toEqual('1px');
      expect(stubStyle.top).toEqual('2px');
      expect(stubStyle.fontFamily).toEqual('Arial');
      
      var reset = {display: '', left: null, top: false, fontFamily: true};
      ReactDOM.render(<div style={reset} />, container);
      expect(stubStyle.display).toEqual('');
      expect(stubStyle.left).toEqual('');
      expect(stubStyle.top).toEqual('');
      expect(stubStyle.fontFamily).toEqual('');
    });
    it('should not update styles when mutating a proxy style object', () => {
      var styleStore = {display: 'none', fontFamily: 'Arial', lineHeight: 1.2};
      
      
      var styles = {
        get display() {