**Do you want to request a *feature* or report a *bug*?**
bug

**What is the current behavior?**
React 15.x was able to render within a DocumentFragment/shadowRoot, not possible with Fiber anymore

**DEMO**

https://www.webpackbin.com/bins/-KvPFG7-HGfQ34IgUxQt

```js
import React, {Component} from 'react'
import {render} from 'react-dom'


class MyComponent extends Component{
  render(){
    return <div>Hello From React !</div>
  }
}

class MyElement extends HTMLElement {
  static is = 'my-element'
  constructor(){
    super()
    const shadowRoot = this.attachShadow({mode:'open'})
    try {
      // this fails 
      render(<MyComponent/>, shadowRoot)
    } catch (e){
      console.error(e)
      shadowRoot.innerHTML = `
        <div style="color:red;">${e}</div>
        <div>see console log for stack trace</div>
       `
    }
  }
  connectedCallback(){
    console.log('MyElement mounted!')
  }
}

customElements.define(MyElement.is, MyElement)
```


related -> https://github.com/skatejs/renderer-react/issues/3

**What is the expected behavior?**
be able to render to shadow root like previous versions of React

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
React 16
Chrome

var listeners = listenersTable.get(node);
      if (listeners) {
        for (var i = 0; i < listeners.length; i++) {
          if (!listeners[i].removed && listeners[i].type === type) return true;
        }
      }
      return false;
    }
    function hasListenerInAncestors(target, type) {
      for (var node = unwrap(target); node; node = node.parentNode) {
        if (hasListener(wrap(node), type)) return true;
      }
      return false;
    }
    if (OriginalEventTarget) registerWrapper(OriginalEventTarget, EventTarget);
    function wrapEventTargetMethods(constructors) {
      forwardMethodsToWrapper(constructors, methodNames);
    }
    var originalElementFromPoint = document.elementFromPoint;
    function elementFromPoint(self, document, x, y) {
      scope.renderAllPending();
      var element = wrap(originalElementFromPoint.call(unsafeUnwrap(document), x, y));
      if (!element) return null;
      var path = getEventPath(element, null);
      var idx = path.lastIndexOf(self);
      if (idx == -1) return null; else path = path.slice(0, idx);
      return eventRetargetting(path, self);
    }
    function getEventHandlerGetter(name) {