Bug 123726 "Top n", "Bottom n" in highlight dialog doesn't work.
Description: "Top n", "Bottom n" in highlight dialog doesn't work. Steps to reproduce: 1. Add a highlight for a table. 2. Set highlight rule: "account_id", "top n", "3", let its font color red. 3. Preview the report, it doesn't work. Attached is design file.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/api/aggregation/Accumulator.java
* the Accumulator to process. There are 3 steps involved in calculating an aggregate value:
 * <p>
 * (1) Start: the Data Engine calls the start() method of the Accumulator upon 
 *  the start of a new range of data rows on which an aggregation is requested<br>
 * (2) OnRow: for each data row in range (after applying the optional filtering condition), the onRow()
 * method is called with values calculated based on the data row. <br>
 * (3) Finish: After the onRow call for the last data row in range, the Data Engine calls the finish()
 * method. <br>
 * <p>
 * For SUMMARY_AGGR type aggregation, the Data Engine calls getValue() after the finish() call to obtain 
 * the value of the aggregation. For RUNNING_AGGR type aggregation, it calls getValue() after each onRow()
 * call. <p>
 * Each instance of the accumulator can be used to calculate aggregations over multiple groups of data. The 
 * implementation should re-initialize the class for a new group in the start() method.
 */
abstract public class Accumulator
{
    
    /**
     * This method is called before the the first onRow() call. This is an opportunity to 
     * initialize any internal data structure. 
     */
    public void start()
    {}
    
    /**
     * This method is called after the last onRow() call. This is an opportunity for the Accumulator 
     * to finalize its calculation, and to release any resource allocated to facilitate the calcuation.
     * getValue() may be called after finish() for SUMMARY_AGGR type of aggregation.
     * @throws DataException