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.
node.removeAttribute.mockImplementation(nodeRemoveAttribute);
      ReactDOM.render(<div id="" />, container);
      expect(node.setAttribute.mock.calls.length).toBe(0);
      expect(node.removeAttribute.mock.calls.length).toBe(0);
      ReactDOM.render(<div id="foo" />, container);
      expect(node.setAttribute.mock.calls.length).toBe(1);
      expect(node.removeAttribute.mock.calls.length).toBe(0);
      ReactDOM.render(<div id="foo" />, container);
      expect(node.setAttribute.mock.calls.length).toBe(1);
      expect(node.removeAttribute.mock.calls.length).toBe(0);
      ReactDOM.render(<div />, container);
      expect(node.setAttribute.mock.calls.length).toBe(1);
      expect(node.removeAttribute.mock.calls.length).toBe(1);
      ReactDOM.render(<div id="" />, container);
      expect(node.setAttribute.mock.calls.length).toBe(2);
      expect(node.removeAttribute.mock.calls.length).toBe(1);
      ReactDOM.render(<div />, container);
      expect(node.setAttribute.mock.calls.length).toBe(2);
      expect(node.removeAttribute.mock.calls.length).toBe(2);
    });
    it('should not incur unnecessary DOM mutations for string properties', () => {
      var container = document.createElement('div');
      ReactDOM.render(<div value="" />, container);
      var node = container.firstChild;
      var nodeValueSetter = jest.genMockFn();
      var oldSetAttribute = node.setAttribute.bind(node);
      node.setAttribute = function(key, value) {
        oldSetAttribute(key, value);
        nodeValueSetter(key, value);
      };