private HashMap collectSubregionSerialNumbers() {
    HashMap map = new HashMap();
    addSubregionSerialNumbers(map);
    return map;
  }
Returns a map of subregion full paths to SerialNumbers. Caller must have acquired the
destroyLock if a stable view is desired. Key is String, value is Integer.

@return HashMap of subregions to SerialNumbers
geode-core/src/main/java/org/apache/geode/internal/cache/LocalRegion.java