React version: 0.0.0-f77c7b9d7

## Steps To Reproduce

1. Mount a component with even listeners in a `ShadowRoot`

Link to code example:

- [codesandbox with `react@next`](https://codesandbox.io/s/next-shadowroot-as-root-element-pkktc) (crashes)
- [codesandbox with `react@16.13.1`](https://codesandbox.io/s/16-shadowroot-as-root-element-m74ob) (mounts  without errors/warnings)


## The current behavior

Throws with 
> ensureListeningTo(): received a container that was not an element node. This is likely a bug in React.

## The expected behavior

1. throw with a descriptive error that ShadowRoot is no longer supported as a root element

or

2. continue to allow ShadowRoot as a root element

No preference here. This was just from an old regression test we had. 

Will be fixed by https://github.com/facebook/react/pull/15894
ReactDOMInputPostMountWrapper(domElement, rawProps, false);
      break;
    case 'textarea':
      
      
      track((domElement: any));
      ReactDOMTextareaPostMountWrapper(domElement, rawProps);
      break;
    case 'option':
      ReactDOMOptionPostMountWrapper(domElement, rawProps);
      break;
    case 'select':
      ReactDOMSelectPostMountWrapper(domElement, rawProps);
      break;
    default:
      if (typeof props.onClick === 'function') {
        
        trapClickOnNonInteractiveElement(((domElement: any): HTMLElement));
      }
      break;
  }
}
export function diffProperties(
  domElement: Element,
  tag: string,
  lastRawProps: Object,
  nextRawProps: Object,
  rootContainerElement: Element | Document,
): null | Array<mixed> {
  if (__DEV__) {