anchor.diff:      if (ignore) return;
       push(_invariantCheckToken);
     }
  +
     void handleQualified(period) {
       debugEvent('Qualified');
       if (ignore) return;
  
positive.code:     push(new Opaque(hint: "call"));
    }
  }
  /// A listener of parser events that builds summary information as parsing
  /// progresses.
  class SummaryBuilder extends StackListener {
  
negative.code: 
    void _unhandledSend();
  }
  
  /// Builder for initializer expressions. These expressions exclude any nested
  /// expression that is not needed to infer strong mode types.
  class InitializerBuilder extends ExpressionListener {
  