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".
expectNode(node, TEXT_NODE_TYPE, text);
    }
    describe('text children', function() {
      itRenders('a div with text', async render => {
        const e = await render(<div>Text</div>);
        expect(e.tagName).toBe('DIV');
        expect(e.childNodes.length).toBe(1);
        expectNode(e.firstChild, TEXT_NODE_TYPE, 'Text');
      });
      itRenders('a div with text with flanking whitespace', async render => {
        
        const e = await render(<div>  Text </div>);
        expect(e.childNodes.length).toBe(1);
        expectNode(e.childNodes[0], TEXT_NODE_TYPE, '  Text ');
      });
      itRenders('a div with an empty text child', async render => {
        const e = await render(<div>{''}</div>);
        expect(e.childNodes.length).toBe(0);
      });
      itRenders('a div with multiple empty text children', async render => {
        const e = await render(<div>{''}{''}{''}</div>);
        if (render === serverRender || render === streamRender) {
          
          
          expect(e.childNodes.length).toBe(0);
          expect(e.textContent).toBe('');
        } else {
          expect(e.childNodes.length).toBe(3);