Register Metrics to make them visible to Observatory.
static void register(Metric metric) {
  ArgumentError.checkNotNull(metric, 'metric');
  if (_metrics[metric.name] != null) {
    throw new ArgumentError('Registered metrics have unique names');
  }
  _metrics[metric.name] = metric;
}
    © 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
    https://api.dart.dev/stable/2.5.0/dart-developer/Metrics/register.html