anchor.diff:  
   import 'dart:async';
   import 'dart:convert';
  -import 'dart:io' show exitCode, stderr;
  +import 'dart:io' show Platform, exitCode, stderr;
   
   import 'package:analyzer/file_system/file_system.dart';
   import 'package:dartdoc/options.dart';
  
positive.code:       },
        (e, chain) {
          if (e is DartdocFailure) {
            stderr.writeln('\ndartdoc failed: $e.');
            exitCode = 1;
          } else {
            stderr.writeln('\ndartdoc failed: $e\n$chain');
            exitCode = 255;
          }
        },
  
negative.code: 
    DartdocResults(this.packageMeta, this.packageGraph, this.outDir);
  }
  
  String get _dartdocFailedMessage =>
      'dartdoc $packageVersion (${Platform.script.path}) failed';
  