private void updateScrollStarts() {
        final int padTop = getPaddingTop();
        final int listHeight = getHeight() - padTop - getPaddingBottom();
        float heightF = (float) listHeight;

        mUpScrollStartYF = padTop + mDragUpScrollStartFrac * heightF;
        mDownScrollStartYF = padTop + (1.0f - mDragDownScrollStartFrac) * heightF;

        mUpScrollStartY = (int) mUpScrollStartYF;
        mDownScrollStartY = (int) mDownScrollStartYF;

        mDragUpScrollHeight = mUpScrollStartYF - padTop;
        mDragDownScrollHeight = padTop + listHeight - mDownScrollStartYF;
    }
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