code: private View findReferenceChildClosestToEnd(RecyclerView.State state) {
          return mShouldReverseLayout ? findFirstReferenceChild(state.getItemCount()) :
                  findLastReferenceChild(state.getItemCount());
      }
docs: Among the children that are suitable to be considered as an anchor child, returns the one
  closest to the end of the layout.
  <p>
  Due to ambiguous adapter updates or children being removed, some children's positions may be
  invalid. This method is a best effort to find a position within adapter bounds if possible.
  <p>
  It also prioritizes children that are within the visible bounds.
  @return A View that can be used an an anchor View.