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
/**
	 * Key to indicate the 'allowPage' control of the preview.
	 */
	public final static String ALLOW_PAGE_KEY = "ALLOW_PAGE_KEY"; 
	/**
	 * Key to indicate the 'servletName' of the preview.
	 */
	public final static String SERVLET_NAME_KEY = "SERVLET_NAME_KEY"; 
	/**
	 * Key to indicate the 'resourceFolder'.
	 */
	public final static String RESOURCE_FOLDER_KEY = "RESOURCE_FOLDER_KEY"; 
	/**
	 * Key to indicate the 'maxRows'
	 */
	public final static String MAX_ROWS_KEY = "MAX_ROWS_KEY"; 
	/**
	 * Key to indicate the 'maxLevelMember'
	 */
	public final static String MAX_CUBELEVELS_KEY = "MAX_CUBELEVELS_KEY"; 
	/**
	 * Property to indicate whether it is a report debug mode
	 */
	public final static String REPORT_DEBUT_MODE = "report_debug_mode"; 
	/**
	 * locale mapping. Save some time.
	 */
	public static TreeMap LocaleTable = null;
	static
	{