anchor.diff:      if (uri.startsWith(FILE_PREFIX)) {
         return resolveSymbolicLinks(p.fromUri(Uri.parse(uri)));
       }
  -    if (uri.startsWith(HTTP_PREFIX)) {
  -      return uri;
  -    }
       // We cannot deal with anything else.
       failed.add(uri);
       return null;
  
positive.code:   static const DART_PREFIX = 'dart:';
    static const PACKAGE_PREFIX = 'package:';
    static const FILE_PREFIX = 'file://';
    static const HTTP_PREFIX = 'http://';
  
    @Deprecated('See packageRoot. Removal in 0.7.0.')
    String get pkgRoot => packageRoot;
  
negative.code: 
    /// Loads an imported resource and returns a [Future] with a [List] of lines.
    /// Returns [null] if the resource could not be loaded.
    Future<List<String>> load(String path) async {
      try {
        return new File(path).readAsLines();
      } catch (_) {
        failed.add(path);
        return null;
      }
    }
  }
  