ItemInfo infoForPosition(int position) {
        for (int i = 0; i < mItems.size(); i++) {
            ItemInfo ii = mItems.get(i);
            if (ii.position == position) {
                return ii;
            }
        }
        return null;
    }
This is the persistent state that is saved by ViewPager.  Only needed
if you are creating a sublass of ViewPager that must save its own
state, in which case it should implement a subclass of this which
contains that state.
library/src/main/java/com/daimajia/slider/library/Tricks/ViewPagerEx.java