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".
constructor(element, makeStaticMarkup) {
    var children = React.isValidElement(element) ? [element] : toArray(element);
    var topFrame = {
      
      
      domNamespace: Namespaces.html,
      children,
      childIndex: 0,
      context: emptyObject,
      footer: '',
    };
    if (__DEV__) {
      topFrame.debugElementStack = [];
    }
    this.stack = [topFrame];
    this.exhausted = false;
    this.currentSelectValue = null;
    this.previousWasTextNode = false;
    this.makeStaticMarkup = makeStaticMarkup;
  }
  read(bytes) {