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".
it('should error reconnecting empty style attribute', () =>
        expectMarkupMismatch(
          <div style={{width: '1px'}} />,
          <div style={{}} />,
        ));
      it('should error reconnecting added style values', () =>
        expectMarkupMismatch(
          <div style={{}} />,
          <div style={{width: '1px'}} />,
        ));
      it('should error reconnecting different style values', () =>
        expectMarkupMismatch(
          <div style={{width: '1px'}} />,
          <div style={{width: '2px'}} />,
        ));
      it('should reconnect number and string versions of a number', () =>
        expectMarkupMatch(
          <div style={{width: '1px', height: 2}} />,
          <div style={{width: 1, height: '2px'}} />,
        ));
      it('should error reconnecting reordered style values', () =>
        expectMarkupMismatch(
          <div style={{width: '1px', fontSize: '2px'}} />,
          <div style={{fontSize: '2px', width: '1px'}} />,
        ));
    });
    describe('text nodes', function() {
      it('should error reconnecting different text', () =>
        expectMarkupMismatch(<div>Text</div>, <div>Other Text</div>));
      it('should reconnect a div with a number and string version of number', () =>