anchor.diff:    * the absolute values are not of much interest; it is the
     * relative values (intervals) that are of interest.
     */
  -  Map _marks;
  +  final Map _marks = {};
   
    /**
     * [_measures] holds a set of intervals of interest. It maps
     * names to elapsed time (in milliseconds).
     */
  -  Map _measures;
  +  final Map _measures = {};
   
    /**
     * [_starts] holds the start times of the intervals. This is
     * useful to tell when the intervals occurred with respect to
     * each other. It maps interval names to start times.
     */
  -  Map _starts;
  +  final Map _starts = {};
   
    /**
     * [_postMessages] is a flag to control whether to use
  
positive.code:         }
        }
      }
      aEpisodes.sort(_sortEpisodes);
  
      // Find start and end of all episodes.
  
negative.code:   const _NullSanitizer();
    void sanitizeTree(Node node) {}
  }
  
  