Chrome ToT r504699, OS R63-9972, link, --mash

Also reproduces on linux desktop

* Open a browser window
* Hit F4 to enter immersive fullscreen
* Put cursor at top of screen

Top views don't slide down. sky@ thinks this used to work. I'm a little surprised, because I expect it would need a global EventHandler/EventFilter to detect the mouse position, like in  issue 631216 .

sky, do you want this? Feel free to reroute.