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
public final static String WebAppPlugin = ViewerPlugin.PLUGIN_ID;
	/**
	 * locale preference name
	 */
	public final static String USER_LOCALE = "user_locale"; 
	/**
	 * Preference key for SVG chart flag.
	 */
	public final static String SVG_FLAG = "svg_flag"; 
	/**
	 * Preference key for master page content flag.
	 */
	public final static String MASTER_PAGE_CONTENT = "master_page_content"; 
	
	public final static String PREVIEW_MAXROW = "preview_maxrow"; 
	
	public final static String PREVIEW_MAXCUBELEVEL = "preview_maxlevelmember"; 
	
	public final static String PREVIEW_MAXINMEMORYCUBESIZE = "preview_maxinmemorycubesize"; 
	
	public static final String VIEWER_PREVIEW = "preview"; 
	
	public static final String VIEWER_FRAMESET = "frameset"; 
	
	public static final String VIEWER_RUN = "run"; 
	
	/**
	 * Key to indicate the format of the preview.
	 */
	public final static String FORMAT_KEY = "FORMAT_KEY";