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".
let parent = e.parentNode;
        if (
          render === serverRender ||
          render === clientRenderOnServerString ||
          render === streamRender
        ) {
          
          
          expect(parent.childNodes.length).toBe(5);
          expectTextNode(parent.childNodes[0], 'a');
          expectTextNode(parent.childNodes[2], 'b');
          expectTextNode(parent.childNodes[4], 'c');
        } else {
          expect(parent.childNodes.length).toBe(3);
          expectTextNode(parent.childNodes[0], 'a');
          expectTextNode(parent.childNodes[1], 'b');
          expectTextNode(parent.childNodes[2], 'c');
        }
      });
    });
    describe('escaping >, <, and &', function() {
      itRenders('>,<, and & as single child', async render => {
        const e = await render(<div>{'<span>Text&quot;</span>'}</div>);
        expect(e.childNodes.length).toBe(1);
        expectNode(e.firstChild, TEXT_NODE_TYPE, '<span>Text&quot;</span>');
      });
      itRenders('>,<, and & as multiple children', async render => {
        const e = await render(
          <div>{'<span>Text1&quot;</span>'}{'<span>Text2&quot;</span>'}</div>,
        );