anchor.diff:  
   import 'dart:async';
   
  -import 'package:json/json.dart';
   
   import '../builder.dart';
   import '../jobs.dart';
   import '../workspace.dart';
   import '../package_mgmt/bower_properties.dart';
  +import 'json_parser.dart';
  +import 'utils.dart';
   
   /**
    * A [Builder] implementation to add validation warnings to JSON files.
  
positive.code: 
  class _JsonParserListener extends JsonListener {
    final File file;
  
    _JsonParserListener(this.file);
  
    void fail(String source, int position, String message) {
      int lineNum = _calcLineNumber(source, position);
      file.createMarker('json', Marker.SEVERITY_ERROR, message, lineNum, position);
    }
  
    /**
     * Count the newlines between 0 and position.
     */
    int _calcLineNumber(String source, int position) {
      int lineCount = 0;
  
      for (int index = 0; index < source.length; index++) {
        if (source[index] == '\n') lineCount++;
        if (index == position) return lineCount + 1;
      }
  
      return lineCount;
    }
  }
  
negative.code: 
        try {
          if (str.trim().isNotEmpty) {
            StringLineOffsets lineOffsets = new StringLineOffsets(str);
            JsonParser parser = new JsonParser(str, new _JsonParserListener(file, lineOffsets));
            parser.parse();
          }
        } catch (e) {
  