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
{
		if ( format == null || format.trim( ).length( ) <= 0
				|| HTM.equalsIgnoreCase( format ) )
			format = HTML;
		String root = null;
		if ( !HTML.equalsIgnoreCase( format ) )
		{
			root = createURL( VIEWER_PREVIEW, report, format, true, null, null,
					null );
		}
		else
		{
			root = createURL( allowPage ? VIEWER_FRAMESET : VIEWER_PREVIEW,
					report, format, true, null, null, null )
					+ "&" + new Random( ).nextInt( ); 
		}
		try
		{
			startWebApp( );
			BrowserAccessor.getPreviewBrowser( false ).displayURL( root );
		}
		catch ( Exception e )
		{
			
		}
	}
	/**
	 * Displays the specified url useing eclipse SWT browser.
	 * 
	 * @param report