code: protected void endDragging(MouseUpEvent event) {
  
          m_dragging = false;
          DOM.releaseCapture(getElement());
          removeStyleName(I_CmsLayoutBundle.INSTANCE.dialogCss().dragging());
      }
docs: Called on mouse up in the caption area, ends dragging by ending event
  capture.
  
  @param event the mouse up event that ended dragging
  
  @see DOM#releaseCapture
  @see #beginDragging
  @see #endDragging