anchor.diff:      if (!_hasTimeline) return;
       // TODO: When NNBD is complete, delete the following line.
       ArgumentError.checkNotNull(name, 'name');
  +    if (!_isDartStreamEnabled()) {
  +      // Stream is disabled.
  +      return;
  +    }
       Map? instantArguments;
       if (arguments != null) {
         instantArguments = new Map.from(arguments);
  
positive.code:     }
      // Pop top item off of stack.
      var block = _stack.removeLast();
      block._finish(arguments);
    }
  
  
negative.code:   final TimelineTask? _parent;
    final String? _filterKey;
    final int _taskId;
    final List<_AsyncBlock?> _stack = [];
  }
  
  /// An asynchronous block of time on the timeline. This block can be kept
  