The implementation of ImmersiveGestureHandler needs to see gestures outside the bounds of the window. It may also end up consuming the events.

See ImmersiveFullscreenController::OnGestureEvent() for details on this, where it calls SetHandled().

sky, do you know how we're going to do immersive mode for SingleProcessMash? Classic ash code or mash code?

We will need to use the mash code for this (because the browser window is backed by the windowservice).

IIUC, the reason ImmersiveGestureHandler needs gestures outside the window bounds is for the case of a bezel sensor, which would produce gesture events located off-screen. Would it make sense for the WM to assume bezel-located events should be sent to the window fullscreened on the nearest display, if any?

Also, I don't know how to simulate gesture events (--touch-devices doesn't seem to do it).