There is some ambiguity about whether ScheduleComposite will necessarily
trigger a composite all the way to nsWindow::DrawWindowUnderlay. Android
robocop tests assume it will, because they rely on DrawWindowOverlay
being called so they can take a screenshot and make progress,
but this is a very fragile assumption. They also rely on the entire
window being painted, which is also a fragile assumption.
This patch improves the situation by explicitly invalidating the current
window area when Android Java code needs to trigger a composite. This avoids
regressions from future patches in this series which make composition bail
out when there is nothing invalid.
The resulting setup is still a bit fragile for my taste but I'm not sure
what the ideal solution would be.
