My application crashes IE9 when I upgrade to React v15.2.0! It works fine with v15.1.0 and all earlier versions.

My diff looks like this

```
package.json
 -    "react-addons-perf": "15.1.0",
 +    "react-addons-perf": "15.2.0",
 -    "react-addons-shallow-compare": "15.1.0",
 +    "react-addons-shallow-compare": "15.2.0",
 -    "react-addons-test-utils": "15.1.0",
 +    "react-addons-test-utils": "15.2.0",
 -    "react": "15.1.0",
 +    "react": "15.2.0",
 -    "react-addons-css-transition-group": "15.1.0",
 +    "react-addons-css-transition-group": "15.2.0",
 -    "react-addons-transition-group": "15.1.0",
 +    "react-addons-transition-group": "15.2.0",
 -    "react-dom": "15.1.0",
 +    "react-dom": "15.2.0",
```

Below is a GIF of the crash, I recorded this using BrowserStack (Win7, IE9). I start the recording with Google loaded and dev tools open, I then navigated to my apps URL. As you can see IE9 just crashes hard with nothing logged to console. All other browsers load my app just fine, this only seems to crash IE9!

![crash](https://cloud.githubusercontent.com/assets/456400/18810916/7694bfd0-829a-11e6-897d-4b70df1972a2.gif)

Did you guys drop support for IE9 in 15.2.0? If not, any ideas what might be causing this?

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