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
String format, boolean inDesigner, String resourceFolder,
			String maxrows, String maxlevels )
	{
		String encodedReportName = null;
		try
		{
			encodedReportName = URLEncoder.encode( report, "utf-8" ); 
		}
		catch ( UnsupportedEncodingException e )
		{
			
		}
		String locale = ViewerPlugin.getDefault( ).getPluginPreferences( )
				.getString( USER_LOCALE );
		String svgFlag = ViewerPlugin.getDefault( ).getPluginPreferences( )
				.getString( SVG_FLAG );
		boolean bSVGFlag = false;
		
		String cubeMemorySize = ViewerPlugin.getDefault( )
				.getPluginPreferences( )
				.getString( PREVIEW_MAXINMEMORYCUBESIZE );
		
		boolean rtl = false;
		String eclipseCommands = System.getProperty( "eclipse.commands" ); 
		if ( eclipseCommands != null )
		{
			String[] options = eclipseCommands.split( "-" ); 
			String regex = "[\\s]*[dD][iI][rR][\\s]*[rR][tT][lL][\\s]*"; 
			Pattern pattern = Pattern.compile( regex );
			for ( int i = 0; i < options.length; i++ )