code: public int getAvailableHeight(int fixedContentHeight) {
  
          if (m_buttonPanel.isVisible()) {
              fixedContentHeight += m_buttonPanel.getOffsetHeight();
          }
          return Window.getClientHeight() - 150 - fixedContentHeight;
      }
docs: Returns the maximum available height inside the popup.<p>
  
  @param fixedContentHeight fixed content height to deduct from the available height
  
  @return the maximum available height