Use contrib/video section

This is an (free software) installer that installs a (non-free) proprietary component. It thus can not exist in the main part of the debian archive. Since it doesn't contain non-free software (but downloads that from internet) it should also not go into non-free area. The software itself is free software, but it's useless without the non-free parts that's downloaded from internet. Thus contrib area.

Since widevine is about (DRM for) video (decoding). Possibly the video section is better than misc.

In other words, I think the correct setting in debian/control is Section: contrib/video.