void start(String name, {Map arguments})

Start a synchronous operation within this task named name. Optionally takes a Map of arguments.

Source 

void start(String name, {Map arguments}) {
  if (_isProduct) {
    return;
  }
  if (name is! String) {
    throw new ArgumentError.value(name,
                                  'name',
                                  'Must be a String');
  }
  var block = new _AsyncBlock._(name, _taskId);
  if (arguments is Map) {
    block._appendArguments(arguments);
  }
  _stack.add(block);
  block._start();
}