Bug 74822 [Preferences] Update spec for property change events
bundles/org.eclipse.jface/src/org/eclipse/jface/util/PropertyChangeEvent.java
*
     * @return the new value, or <code>null</code> if not known
     *  or not relevant
     */
    public Object getNewValue() {
        return newValue;
    }
    /**
     * Returns the old value of the property.
     *
     * @return the old value, or <code>null</code> if not known
     *  or not relevant
     */
    public Object getOldValue() {
        return oldValue;
    }
    /**
     * Returns the name of the property that changed.
     * <p>
     * Warning: there is no guarantee that the property name returned
     * is a constant string.  Callers must compare property names using
     * equals, not ==.
     * </p>
     *
     * @return the name of the property that changed
     */
    public String getProperty() {
        return propertyName;
    }
}