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.
var firstChild = ((div.firstChild: any): HTMLScriptElement);
        domElement = div.removeChild(firstChild);
      } else if (props.is) {
        
        domElement = ownerDocument.createElement(type, {is: props.is});
      } else {
        
        
        
        domElement = ownerDocument.createElement(type);
      }
    } else {
      domElement = ownerDocument.createElementNS(namespaceURI, type);
    }
    if (__DEV__) {
      if (namespaceURI === HTML_NAMESPACE) {
        if (
          !isCustomComponentTag &&
          Object.prototype.toString.call(domElement) ===
            '[object HTMLUnknownElement]' &&
          !Object.prototype.hasOwnProperty.call(warnedUnknownTags, type)
        ) {
          warnedUnknownTags[type] = true;
          warning(
            false,
            'The tag <%s> is unrecognized in this browser. ' +
              'If you meant to render a React component, start its name with ' +
              'an uppercase letter.',
            type,