@Override
    public int compare(Change o1, Change o2) {
      ContentRevision bRev1 = o1.getBeforeRevision();
      ContentRevision bRev2 = o2.getBeforeRevision();
      int delta = compareRevisions(bRev1, bRev2);
      if (delta != 0) return delta;

      ContentRevision aRev1 = o1.getAfterRevision();
      ContentRevision aRev2 = o2.getAfterRevision();
      return compareRevisions(aRev1, aRev2);
    }
@Override
    public int compare(Change o1, Change o2)