Previously it was safe to call setFastScrollEnabled() and setFastScrollAlwaysVisible() off the UI thread. After switching FastScroller to use an Overlay, these methods stopped working. This change ensures that all direct interaction with FastScroller happens on the thread that created the host AbsListView. BUG: 10210504 Change-Id: Ib6d9bd9212965420c0de39546652e3bc2d32ff8b