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.
}
        } else if (propKey === STYLE) {
          
          extraAttributeNames.delete(propKey);
          const expectedStyle = CSSPropertyOperations.createDangerousStringForStyles(
            nextProp,
          );
          serverValue = domElement.getAttribute('style');
          if (expectedStyle !== serverValue) {
            warnForPropDifference(propKey, serverValue, expectedStyle);
          }
        } else if (isCustomComponentTag) {
          
          extraAttributeNames.delete(propKey.toLowerCase());
          serverValue = DOMPropertyOperations.getValueForAttribute(
            domElement,
            propKey,
            nextProp,
          );
          if (nextProp !== serverValue) {
            warnForPropDifference(propKey, serverValue, nextProp);