Bug 209119 Need WebViewer provide cancel function
Need WebViewer provide a cancel function, this will be used to cancel current report execution during designer preview.
viewer/org.eclipse.birt.report.viewer/src/org/eclipse/birt/report/viewer/utilities/WebViewer.java
browser.setUrl( createURL( servletName, report, format, true, null,
				null, null )
				+ "&" + new Random( ).nextInt( ) ); 
	}
	/**
	 * Displays the specified url using eclipse SWT browser.
	 * 
	 * @param report
	 *            report report
	 * @param browser
	 *            SWT browser instance
	 * @param params
	 *            the parameter map to set
	 */
	public static void display( String report, Browser browser, Map params )
	{
		startWebApp( );
		browser.setUrl( createURL( report, params )
				+ "&" + new Random( ).nextInt( ) ); 
	}
	/**
	 * Displays the specified url using eclipse SWT browser.
	 * 
	 * @param report
	 *            report report
	 * @param params
	 *            the parameter map to set
	 */
	public static void display( String report, Map params )
	{