private @NotNull LineSet updateInsideOneLine(int line, int lengthDelta) {
    int[] starts = myStarts.clone();
    for (int i = line + 1; i < starts.length; i++) {
      starts[i] += lengthDelta;
    }

    byte[] flags = myFlags.clone();
    flags[line] |= MODIFIED_MASK;
    return new LineSet(starts, flags, myLength + lengthDelta);
  }
private @NotNull LineSet updateInsideOneLine(int line, int lengthDelta)