@Override
        public float getSpeed(float w, long t) {
            return mMaxScrollSpeed * w;
        }
Defines the scroll speed during a drag-scroll. User can
provide their own; this default is a simple linear profile
where scroll speed increases linearly as the floating View
nears the top/bottom of the ListView.
third_party/DragSortListView/src/com/mobeta/android/dslv/DragSortListView.java