screen sharing doesn't work on chrome

[bhackett1024]

STR:

1. open chrome (version 90) and visit https://www.webrtc-experiment.com/Pluginfree-Screen-Sharing
2. click "share your screen", pick any window or tab on the machine
3. copy URL and paste into a new tab
4. video loads, but it is all white
5. paste same URL into firefox (version 87), and video loads as expected

I get the same behavior on both macOS 10.15 and ubuntu linux.

[hbenl]

I tried on Arch Linux with Chromium 89.0.4389.90 and I get the exact same behavior.

[opencoca]

Replicated on big sur 11.16 and El Capitan 10.11.16.

Screen sharing is working well on other open source WebRTC platforms.