I have a Dell XPS 13 (9343, 2015 developer edition) with Ubuntu 16.04 and VirtualBox. I created a Windows 10 client and want to test a Windows app with webcam support.

Step 1. Install “Oracle VM VirtualBox Extension Pack”
Before this is installed, if you run command VBoxManage list webcams, you will get error:

VboxMange: error: No extension pack by the name ‘Oracle VM VirtualBox Extension Pack’ was found.

You can download this Extension Pack from virtualbox.org. After it’s installed, running VBoxManage list webcams will find the cam and its result is like:

Video Input Devices: 1
.1 “Integrated_Webcam_Hd”
/dev/video0

Step 2. Start the Windows 10 client, then in VirtualBox’s Devices menu, there is Webcams, check it.
Now Windows will automatically set up this new device. After all are set up, you can run Windows “Camera” app to verify it works.