Bug 211703 Support muti-view on report item.
As title described.
xtab/org.eclipse.birt.report.item.crosstab.core/src/org/eclipse/birt/report/item/crosstab/core/de/internal/CrosstabReportItemTask.java
/**
	 * Adds a new element as the view.
	 * 
	 * @param viewElement
	 *            the element
	 * @throws SemanticException
	 */
	public void addView( DesignElementHandle viewElement )
			throws SemanticException
	{
		MultiViewsHandle multiView = getMultiViews( );
		CommandStack stack = crosstab.getModuleHandle( ).getCommandStack( );
		stack.startTrans( null );
		try
		{
			if ( multiView == null )
			{
				multiView = crosstab.getModuleHandle( ).getElementFactory( )
						.newMultiView( );
				crosstab.getModelHandle( ).setProperty( MULTI_VIEWS_PROP,
						multiView );
			}
			multiView.addView( viewElement );
		}
		catch ( SemanticException e )
		{
			stack.rollback( );
			throw e;
		}
		stack.commit( );