**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

nonEnumerableDataDescriptor.value = value;
      defineProperty(object, name, nonEnumerableDataDescriptor);
    }
    getOwnPropertyNames(window);
    function getWrapperConstructor(node) {
      var nativePrototype = node.__proto__ || Object.getPrototypeOf(node);
      var wrapperConstructor = constructorTable.get(nativePrototype);
      if (wrapperConstructor) return wrapperConstructor;
      var parentWrapperConstructor = getWrapperConstructor(nativePrototype);
      var GeneratedWrapper = createWrapperConstructor(parentWrapperConstructor);
      registerInternal(nativePrototype, GeneratedWrapper, node);
      return GeneratedWrapper;
    }
    function addForwardingProperties(nativePrototype, wrapperPrototype) {
      installProperty(nativePrototype, wrapperPrototype, true);
    }
    function registerInstanceProperties(wrapperPrototype, instanceObject) {
      installProperty(instanceObject, wrapperPrototype, false);
    }
    var isFirefox = /Firefox/.test(navigator.userAgent);
    var dummyDescriptor = {
      get: function() {},
      set: function(v) {},
      configurable: true,
      enumerable: true
    };
    function isEventHandlerName(name) {
      return /^on[a-z]+$/.test(name);
    }
    function isIdentifierName(name) {