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.
warnForDeletedHydratableElement(
    parentNode: Element | Document,
    child: Element,
  ) {
    if (__DEV__) {
      if (didWarnInvalidHydration) {
        return;
      }
      didWarnInvalidHydration = true;
      warning(
        false,
        'Did not expect server HTML to contain a <%s> in <%s>.',
        child.nodeName.toLowerCase(),
        parentNode.nodeName.toLowerCase(),
      );
    }
  },
  warnForDeletedHydratableText(parentNode: Element | Document, child: Text) {
    if (__DEV__) {
      if (didWarnInvalidHydration) {
        return;
      }
      didWarnInvalidHydration = true;
      warning(
        false,
        'Did not expect server HTML to contain the text node "%s" in <%s>.',
        child.nodeValue,
        parentNode.nodeName.toLowerCase(),
      );
    }