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".
if (__DEV__) {
    checkPropTypes(typeSpecs, values, location, 'Component', getStackAddendum);
  }
}
function processContext(type, context) {
  var maskedContext = maskContext(type, context);
  if (__DEV__) {
    if (type.contextTypes) {
      checkContextTypes(type.contextTypes, maskedContext, 'context');
    }
  }
  return maskedContext;
}
var STYLE = 'style';
var RESERVED_PROPS = {
  children: null,
  dangerouslySetInnerHTML: null,
  suppressContentEditableWarning: null,
};
function createOpenTagMarkup(