TimelineTask.withTaskId constructor
Create a task with an explicit taskId. This is useful if you are
passing a task from one isolate to another.
Important note: only provide task IDs which have been obtained as a result of invoking TimelineTask.pass. Specifying a custom ID can lead to ID collisions, resulting in incorrect rendering of timeline events.
If filterKey is provided, a property named filterKey will be inserted
into the arguments of each event associated with this task. The
filterKey will be set to the value of filterKey.
Implementation
TimelineTask.withTaskId(int taskId, {String? filterKey})
  : _parent = null,
    _filterKey = filterKey,
    _taskId = taskId {
  // TODO: When NNBD is complete, delete the following line.
  ArgumentError.checkNotNull(taskId, 'taskId');
}