Observed this on react@16.0.0-beta.5

```js
import React from 'react';
import { renderToString } from 'react-dom/server';

const B = () => 'b';

console.log(renderToString(<div>{'a'}<B />{'c'}</div>));
```

This renders as `<div data-reactroot="">a<!-- -->bc</div>`. If you try to hydrate this you'll get the error: Text content did not match. Server: "bc" Client: "b".
const domElement = await serverRender(serverElement);
  resetModules();
  return renderIntoDom(
    clientElement,
    domElement.parentNode,
    true,
    shouldMatch ? 0 : 1,
  );
}
function expectMarkupMatch(serverElement, clientElement) {
  return testMarkupMatch(serverElement, clientElement, true);
}
function expectMarkupMismatch(serverElement, clientElement) {
  return testMarkupMatch(serverElement, clientElement, false);
}
function resetModules() {