public void setDragScrollStarts(float upperFrac, float lowerFrac) {
        if (lowerFrac > 0.5f) {
            mDragDownScrollStartFrac = 0.5f;
        } else {
            mDragDownScrollStartFrac = lowerFrac;
        }

        if (upperFrac > 0.5f) {
            mDragUpScrollStartFrac = 0.5f;
        } else {
            mDragUpScrollStartFrac = upperFrac;
        }

        if (getHeight() != 0) {
            updateScrollStarts();
        }
    }
Set the width of each drag scroll region by specifying
a fraction of the ListView height.

@param upperFrac Fraction of ListView height for up-scroll bound.
Capped at 0.5f.
@param lowerFrac Fraction of ListView height for down-scroll bound.
Capped at 0.5f.
third_party/DragSortListView/src/com/mobeta/android/dslv/DragSortListView.java