**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 function() {
        var inlineEventHandlers = eventHandlersTable.get(this);
        return inlineEventHandlers && inlineEventHandlers[name] && inlineEventHandlers[name].value || null;
      };
    }
    function getEventHandlerSetter(name) {
      var eventType = name.slice(2);
      return function(value) {
        var inlineEventHandlers = eventHandlersTable.get(this);
        if (!inlineEventHandlers) {
          inlineEventHandlers = Object.create(null);
          eventHandlersTable.set(this, inlineEventHandlers);
        }
        var old = inlineEventHandlers[name];
        if (old) this.removeEventListener(eventType, old.wrapped, false);
        if (typeof value === "function") {
          var wrapped = function(e) {
            var rv = value.call(this, e);
            if (rv === false) e.preventDefault(); else if (name === "onbeforeunload" && typeof rv === "string") e.returnValue = rv;
          };
          this.addEventListener(eventType, wrapped, false);
          inlineEventHandlers[name] = {
            value: value,
            wrapped: wrapped
          };
        }
      };
    }
    scope.elementFromPoint = elementFromPoint;
    scope.getEventHandlerGetter = getEventHandlerGetter;