anchor.diff:      return _treeHashCache;
     }
     
  -  /**
  -  * Generate Map object from DartProgram instance and is required to make it
  -  * possible to convert a DartProgram instance to an JSON string.
  -  */
     Map<String, Object> toJson() {
       _log("Running toJson() for $name");
       
  
positive.code: part of distributed_dart;
  
  /// Represents a file in the tree which can have dependencies. (e.g. Dart file)
  class DartProgram extends DependencyNode {
    static const String _NAME = "name";
    static const String _PATH = "path";
    static const String _HASH = "hash";
    static const String _DEPENDENCIES = "dependencies";
    
    factory DartProgram.fromJson(String jsonString) {
      return new DartProgram.fromMap(json.parse(jsonString));
    }
    
    factory DartProgram.fromMap(Map jsonMap) {
      List<FileNode> dependencies = new List<FileNode>();
      
  
negative.code:   String _treeHashCache = null;
    
    /**
     * Returns a calculated SHA1 checksum for the [DartProgram] object and all the 
     * dependencies.  The purpose of this checksum is to make sure the checksum 
     * is different if there are changes in one of the dependencies.
     */
    String get treeHash {
      if (_treeHashCache == null) {
  