anchor.diff:  
     Uri _cachedFallbackUri;
   
  -  FastUri(this._text, this._scheme, this._path, this._lastSlashIndex);
  +  FastUri._(this._cacheGeneration, this._text, this._scheme, this._path,
  +      this._lastSlashIndex);
   
     @override
     String get authority => '';
  
positive.code:    * of [FastUri] or [Uri] is returned for the same [text].
     */
    static Uri parse(String text) {
      // TODO(scheglov) clear the cache if it is too big
      Uri uri = _cache[text];
      if (uri == null) {
        uri = _parse(text);
        uri ??= Uri.parse(text);
        _cache[text] = uri;
      }
      return uri;
    }
  
negative.code:     if (path.startsWith('//')) {
        path = path.substring(2);
      }
      return new FastUri._(
          _currentCacheGeneration, text, scheme, path, lastSlashIndex);
    }
  }
  