Currently, there exist two descendants of the ScrollbarAnimationController class in CC: ScrollbarAnimationControllerLinearFade for Android scrollbars and ScrollbarAnimationControllerThinning for Aura overlay scrollbars. The two have similar duties, the difference being the timing constants and the addition of a "thinning/expanding" animation in the latter for when the mouse moves near the scrollbars. Since so much is shared, it would make more sense to merge the two classes and make the behavior differences parameters.