Allow Bluetooth access

I'm trying to get `Nearby Sharing` working without much success. ~~On one occasion `chrome://nearby` somehow listed some users but not my own device.~~ **edit:** actually those were example devices appearing after some time.

Bluetooth is a precondition for testing this feature so it might be a good idea to enable this by adding:

```
- --allow=bluetooth
- --system-talk-name=org.bluez
```

I tested Chrome with the `Web Bluetooth API` sample [here](https://googlechrome.github.io/samples/web-bluetooth/device-info.html?allDevices=true) which needs the `Experimental Web Platform features` Chrome flag enabled.
The linked sample test code actually only needs the `system-talk-name` permission and doesn't work with just the `allow` permission, not sure what's going on there.