anchor.diff:    noSuchMethod(Invocation m) => reflect(_original).delegate(m);
   
     // form TransformLogger:
  -  void warning(String message, [Span span]) => _write('warning', message, span);
  -
  -  void error(String message, [Span span]) => _write('error', message, span);
  +  void warning(String message, {AssetId asset, Span span})
  +      => _write('warning', message, span);
  +
  +  void error(String message, {AssetId asset, Span span})
  +      => _write('error', message, span);
   
     void _write(String kind, String message, Span span) {
       _messages.add(_formatter(kind, message, span));
  
positive.code:       // elements. Is there another way we can handle this warning that won't
        // generate false positives?
        _logger.warning('definition for Polymer element with tag name '
            '"$customTagName" not found.', node.sourceSpan);
        return;
      }
  
  
negative.code:       _logger.warning(
            'custom element "$customTagName" extends from "$baseTag". '
            'Did you mean to write <$baseTag is="$customTagName">?',
            span: node.sourceSpan);
      }
    }
  
  