navigator.mediaDevices.enumerateDevices including dummy audio devices.

[Vinayak V Kulkarni]

Steps to reproduce:
1. Open 
https://webrtc.github.io/samples/src/content/devices/input-output/ or
https://guidou.github.io/enumdemo.html page on chrome and check for the devices available.
2. Connect a USB dock (with ports for Audio Input and Output devices) to your laptop, without connecting any audio devices.
3. Open the pages again and check for the devices available
3. In the list of the devices you can see that USB PnP Audio Device are listed.

These devices are dummy devices and do not correspond to any working device and do not provide any audio stream or audio output functionality.

navigator.mediaDevices.enumerateDevices() output also shows the same output. 
Attaching the screenshot and the logs to the conversation. Please see the difference between before plugging in and after plugging in the USB dock.

Please let me know if there is any open bug to track this.

Thanks,
Vinayak