code: public static <E extends Comparable> List<E> toSortedListKeyComparable(Counter<E> c) {
      List<E> l = new ArrayList<E>(c.keySet());
      Collections.sort(l, toComparatorWithKeys(c));
      Collections.reverse(l);
      return l;
    }
docs: A List of the keys in c, sorted from highest count to lowest.
  
  @return A List of the keys in c, sorted from highest count to lowest.