**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

Object.defineProperty(HTMLElement.prototype, name, {
        value: function() {
          scope.renderAllPending();
          return unsafeUnwrap(this)[name].apply(unsafeUnwrap(this), arguments);
        },
        configurable: true,
        enumerable: true
      });
    }
    [ "getBoundingClientRect", "getClientRects", "scrollIntoView" ].forEach(methodRequiresRendering);
    registerWrapper(OriginalHTMLElement, HTMLElement, document.createElement("b"));
    scope.wrappers.HTMLElement = HTMLElement;
    scope.getInnerHTML = getInnerHTML;
    scope.setInnerHTML = setInnerHTML;
  })(window.ShadowDOMPolyfill);
  (function(scope) {
    "use strict";
    var HTMLElement = scope.wrappers.HTMLElement;
    var mixin = scope.mixin;
    var registerWrapper = scope.registerWrapper;
    var unsafeUnwrap = scope.unsafeUnwrap;
    var wrap = scope.wrap;
    var OriginalHTMLCanvasElement = window.HTMLCanvasElement;
    function HTMLCanvasElement(node) {