@NotNull
  public static FrameDiffTool.DiffViewer createViewer(@NotNull DiffContext context,
                                                      @NotNull ContentDiffRequest request) {
    return new DirDiffViewer(context, request);
  }
@NotNull
  public static FrameDiffTool.DiffViewer createViewer(@NotNull DiffContext context,
                                                      @NotNull ContentDiffRequest request)