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".
var contextTypes = type.contextTypes;
  if (!contextTypes) {
    return emptyObject;
  }
  var maskedContext = {};
  for (var contextName in contextTypes) {
    maskedContext[contextName] = context[contextName];
  }
  return maskedContext;
}
function checkContextTypes(typeSpecs, values, location: string) {