**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
case DOCUMENT_NODE:
      case DOCUMENT_FRAGMENT_NODE: {
        type = nodeType === DOCUMENT_NODE ? '#document' : '#fragment';
        let root = (rootContainerInstance: any).documentElement;
        namespace = root ? root.namespaceURI : getChildNamespace(null, '');
        break;
      }
      default: {
        const container: any =
          nodeType === COMMENT_NODE
            ? rootContainerInstance.parentNode
            : rootContainerInstance;
        const ownNamespace = container.namespaceURI || null;
        type = container.tagName;
        namespace = getChildNamespace(ownNamespace, type);
        break;
      }
    }
    if (__DEV__) {
      const validatedTag = type.toLowerCase();
      const ancestorInfo = updatedAncestorInfo(null, validatedTag, null);
      return {namespace, ancestorInfo};
    }
    return namespace;
  },
  getChildHostContext(
    parentHostContext: HostContext,
    type: string,
  ): HostContext {
    if (__DEV__) {