increment method

GroupTracker increment([
  1. int by = 1
])

Implementation

GroupTracker increment([int by = 1]) => GroupTracker._create(
  {
    for (var MapEntry(key: groupRef, value: position) in _positions.entries)
      groupRef: position + by,
  },
  _groupCount + by,
  _previouslyIgnoredRefs,
);