**Do you want to request a *feature* or report a *bug*?**
bug

**What is the current behavior?**
If there is a client/server mismatch for text inside of an a or button element, it causes it to be automatically focused on page load.

**If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem via https://jsfiddle.net or similar (template for React 16: https://jsfiddle.net/Luktwrdm/, template for React 15: https://jsfiddle.net/hmbg7e9w/).**
```
let text;
let URL = '/randomURL';
if (typeof window !== 'undefined') {
  text = 'CLIENT TEXT';
} else {
  text = 'TEXT';
}

return (
  <a href={URL}>
    {text}
  </a>
);
```

if the focus is not on the window (i.e. if a dom element is selected in the chrome inspector or react inspector widnow), then it doesn't add the focus.

**What is the expected behavior?**
The expected behavior is that it would either show CLIENT TEXT or TEXT (depending on how React16 resolves the diff), but for it not to be automatically highlighted 

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
React16 / macosx / chrome + ff + safari
return str && str.replace(/\(at .+?:\d+\)/g, '(at **)');
}
describe('ReactDOMServer', () => {
  beforeEach(() => {
    jest.resetModules();
    React = require('react');
    ReactCallReturn = require('react-call-return');
    ReactDOM = require('react-dom');
    ReactTestUtils = require('react-dom/test-utils');
    PropTypes = require('prop-types');
    ReactDOMServer = require('react-dom/server');
  });
  describe('renderToString', () => {
    it('should generate simple markup', () => {
      const response = ReactDOMServer.renderToString(<span>hello world</span>);
      expect(response).toMatch(
        new RegExp('<span data-reactroot=""' + '>hello world</span>'),
      );
    });
    it('should generate simple markup for self-closing tags', () => {
      const response = ReactDOMServer.renderToString(<img />);
      expect(response).toMatch(new RegExp('<img data-reactroot=""' + '/>'));
    });
    it('should generate comment markup for component returns null', () => {
      class NullComponent extends React.Component {