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

bug

**What is the current behavior?**

When hydrating a pre-rendered component that uses `dangerouslySetInnerHTML`, + an object with a `toString` method, we get a warning such as:

```
Warning: Did not expect server HTML to contain the text node "Bonjour" in <p>.
```

The component will also appear blank.

This is noteworthy since:
- The markup returned by `render` appears to be correct, meaning:
  - The markup that an SSR server returns is correct
  - The markup that appears on page if we just use `render` on the client, without SSR is correct
- It's only if we do both, that we get errors.

**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/).**

https://codesandbox.io/s/vqkq34o965

(Code, for posterity:)
```js
import React from "react";
import { hydrate } from "react-dom";

const HelloObj = {
  toString: () => "Bonjour"
};

const MyComponent = () => (
  <p
    dangerouslySetInnerHTML={{
      __html: HelloObj
    }}
  />
);

hydrate(<MyComponent />, document.getElementById("app"));
```

**What is the expected behavior?**

The component is not blank, and no error is outputted in the console

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

- react/react-dom 16.2.0
  - This worked < 16 (confirmed working in 15.6.1, if we use the `render` method)
- Chrome Version 62.0.3202.94
- OS X 10.12.6
return instance;
}
export function prepareForCommit(containerInfo: Container): void {
  eventsEnabled = ReactBrowserEventEmitter.isEnabled();
  selectionInformation = ReactInputSelection.getSelectionInformation();
  ReactBrowserEventEmitter.setEnabled(false);
}
export function resetAfterCommit(containerInfo: Container): void {
  ReactInputSelection.restoreSelection(selectionInformation);
  selectionInformation = null;
  ReactBrowserEventEmitter.setEnabled(eventsEnabled);
  eventsEnabled = null;
}
export function createInstance(
  type: string,
  props: Props,
  rootContainerInstance: Container,
  hostContext: HostContext,
  internalInstanceHandle: Object,
): Instance {
  let parentNamespace: string;