int getDecScrollButtonHeight() {
      ScrollBarUI barUI = getUI();
      Insets insets = getInsets();
      int top = Math.max(0, insets.top);
      if (barUI instanceof ButtonlessScrollBarUI) {
        return top + ((ButtonlessScrollBarUI)barUI).getDecrementButtonHeight();
      }
      if (barUI instanceof BasicScrollBarUI) {
        try {
          JButton decrButtonValue = (JButton)BasicScrollBarUiButtonHolder.decrButtonField.invoke(barUI);
          LOG.assertTrue(decrButtonValue != null);
          return top + decrButtonValue.getHeight();
        }
        catch (Throwable e) {
          throw new IllegalStateException(e);
        }
      }
      return top + 15;
    }
int getDecScrollButtonHeight()