**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 setTreeScope = scope.setTreeScope;
    var unsafeUnwrap = scope.unsafeUnwrap;
    var unwrap = scope.unwrap;
    var unwrapIfNeeded = scope.unwrapIfNeeded;
    var wrap = scope.wrap;
    var wrapIfNeeded = scope.wrapIfNeeded;
    var wrappers = scope.wrappers;
    function assertIsNodeWrapper(node) {
      assert(node instanceof Node);
    }
    function createOneElementNodeList(node) {
      var nodes = new NodeList();
      nodes[0] = node;
      nodes.length = 1;
      return nodes;
    }
    var surpressMutations = false;
    function enqueueRemovalForInsertedNodes(node, parent, nodes) {
      enqueueMutation(parent, "childList", {
        removedNodes: nodes,
        previousSibling: node.previousSibling,
        nextSibling: node.nextSibling
      });
    }
    function enqueueRemovalForInsertedDocumentFragment(df, nodes) {
      enqueueMutation(df, "childList", {
        removedNodes: nodes
      });
    }
    function collectNodes(node, parentNode, previousNode, nextNode) {