void ScrollbarActivity::WillRefresh(TimeStamp aTime) { NS_ASSERTION(mIsActive, "should only fade while scrollbars are visible"); NS_ASSERTION(!IsActivityOngoing(), "why weren't we unregistered from the refresh driver when scrollbar activity started?"); NS_ASSERTION(mIsFading, "should only animate fading during fade"); if (!UpdateOpacity(aTime)) { return; } if (!IsStillFading(aTime)) { EndFade(); } }