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.
)}
          </math>
          <p {...expectHTML} />
        </div>,
      );
      assertNamespacesMatch(
        <math {...expectMath}>
          <mi {...expectMath} />
          {usePortal(
            <svg {...expectSVG}>
              <image {...expectSVG} />
              <foreignObject {...expectSVG}>
                <p {...expectHTML} />
                <math {...expectMath}>
                  <mi {...expectMath} />
                </math>
                <p {...expectHTML} />
              </foreignObject>
              <image {...expectSVG} />
            </svg>,
          )}
          <mi {...expectMath} />
        </math>,
      );
      assertNamespacesMatch(
        <div {...expectHTML}>
          {usePortal(
            <svg {...expectSVG}>
              {usePortal(<div {...expectHTML} />)}
              <image {...expectSVG} />