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('gives source code refs for unknown prop warning for exact elements', () => {
      spyOn(console, 'error');
      ReactTestUtils.renderIntoDocument(
        <div className="foo1">
          <div class="foo2" />
          <div onClick="foo3" />
          <div onclick="foo4" />
          <div className="foo5" />
          <div className="foo6" />
        </div>,
      );
      expectDev(console.error.calls.count()).toBe(2);
      expectDev(console.error.calls.argsFor(0)[0]).toContain('className');
      var matches = console.error.calls.argsFor(0)[0].match(/.*\(.*:(\d+)\).*/);
      var previousLine = matches[1];
      expectDev(console.error.calls.argsFor(1)[0]).toContain('onClick');
      matches = console.error.calls.argsFor(1)[0].match(/.*\(.*:(\d+)\).*/);
      var currentLine = matches[1];
      
      
      expect(parseInt(previousLine, 10) + 2).toBe(parseInt(currentLine, 10));
    });
    it('gives source code refs for unknown prop warning for exact elements (ssr)', () => {
      spyOn(console, 'error');
      ReactDOMServer.renderToString(
        <div className="foo1">
          <div class="foo2" />
          <div onClick="foo3" />
          <div onclick="foo4" />