anchor.diff:                       'b',
                        category,
                        name,
  -                     _argumentsAsJson(arguments));
  +                     _argumentsAsJson(_arguments));
     }
   
     // Emit the finish event.
  
positive.code:                          _getTraceClock(),
                           category,
                           name,
                           _argumentsAsJson(arguments));
    }
  }
  
  
negative.code:     }
      var block = new _AsyncBlock._(name, _taskId);
      if (arguments is Map) {
        block._appendArguments(arguments);
      }
      _stack.add(block);
      block._start();
  