[traffxml] Purge expired messages

Signed-off-by: mvglasow <michael -at- vonglasow.com>

traffxml/traff_assessment_tool/mainwindow.hpp

@@ -41,6 +41,11 @@ private:
    */
   void OnOpenTrafficSample();
 
+  /**
+   * Called when the user requests to purge expired messages.
+   */
+  void OnPurgeExpiredMessages();
+
   /**
    * Called when the user requests to clear the cache.
    */