From comments on https://bugs.chromium.org/p/chromium/issues/detail?id=689017#c8:

"The auto-sleep function of host O.S. won't kick in if you closed a tab that had a webRTC peerconnection.  You pretty much have to shut down all chrome tabs.  (Or do not close the tab and instead navigate that tab to a website that doesn't make any webRTC connections.)"

"[This] prevents sleep on devices that should otherwise be sleeping. This was not an issue before either. Looks like the initial report was on OSX, this is happening on Windows 10 as well."

Not sure who the right owner is, so adding Blink>WebRTC and Blink>GetUserMedia components.