function diff (o, n) {
    let diff, output, text;
    diff = new DiffMatchPatch();
    output = diff.DiffMain(o, n);
    diff.diffCleanupEfficiency(output);
    text = diff.diffPrettyHtml(output);

    return text;
  }
Reorder and merge like edit sections.  Merge equalities.
Any edit section can move as long as it doesn't cross an equality.
@param {!Array.<!DiffMatchPatch.Diff>} diffs Array of diff tuples.