addError method
override
    Adds an error to the sink.
Must not be called on a closed sink.
Implementation
void addError(error, [StackTrace stackTrace]) {
  _sink.addError(error, stackTrace);
}Adds an error to the sink.
Must not be called on a closed sink.
void addError(error, [StackTrace stackTrace]) {
  _sink.addError(error, stackTrace);
}