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 validate against multiple children props', () => {
      ReactDOM.render(<div />, container);
      expect(function() {
        ReactDOM.render(
          <div children="" dangerouslySetInnerHTML={{__html: ''}} />,
          container,
        );
      }).toThrowError(
        'Can only set one of `children` or `props.dangerouslySetInnerHTML`.',
      );
    });
    it('should warn about contentEditable and children', () => {
      spyOn(console, 'error');
      ReactDOM.render(<div contentEditable={true}><div /></div>, container);
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(console.error.calls.argsFor(0)[0]).toContain('contentEditable');
    });
    it('should validate against invalid styles', () => {
      ReactDOM.render(<div />, container);
      expect(function() {
        ReactDOM.render(<div style={1} />, container);
      }).toThrowError(
        'The `style` prop expects a mapping from style properties to values, ' +
          "not a string. For example, style={{marginRight: spacing + 'em'}} " +
          'when using JSX.',
      );
    });
    it('should report component containing invalid styles', () => {
      class Animal extends React.Component {