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 e = await render(<input type="checkbox" checked={true} />, 1);
          expect(e.checked).toBe(true);
        },
      );
      itRenders('a checkbox with defaultChecked', async render => {
        const e = await render(<input type="checkbox" defaultChecked={true} />);
        expect(e.checked).toBe(true);
        expect(e.getAttribute('defaultChecked')).toBe(null);
      });
      itRenders(
        'a checkbox checked overriding defaultChecked',
        async render => {
          const e = await render(
            <input
              type="checkbox"
              checked={true}
              defaultChecked={false}
              readOnly={true}
            />,
            1,
          );
          expect(e.checked).toBe(true);
          expect(e.getAttribute('defaultChecked')).toBe(null);
        },
      );
      itRenders(
        'a checkbox checked overriding defaultChecked no matter the prop order',
        async render => {
          const e = await render(
            <input