**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

return getTreeScope(this.host).renderer;
      },
      invalidate: function() {
        if (!this.dirty) {
          this.dirty = true;
          var parentRenderer = this.parentRenderer;
          if (parentRenderer) parentRenderer.invalidate();
          pendingDirtyRenderers.push(this);
          if (renderTimer) return;
          renderTimer = window[request](handleRequestAnimationFrame, 0);
        }
      },
      distribution: function(root) {
        this.resetAllSubtrees(root);
        this.distributionResolution(root);
      },
      resetAll: function(node) {
        if (isInsertionPoint(node)) resetDistributedNodes(node); else resetDestinationInsertionPoints(node);
        this.resetAllSubtrees(node);
      },
      resetAllSubtrees: function(node) {
        for (var child = node.firstChild; child; child = child.nextSibling) {
          this.resetAll(child);
        }
        if (node.shadowRoot) this.resetAll(node.shadowRoot);
        if (node.olderShadowRoot) this.resetAll(node.olderShadowRoot);
      },
      distributionResolution: function(node) {
        if (isShadowHost(node)) {