code: function SamplingRule(name, priority, rate, reservoirSize,
                        host, httpMethod, urlPath, serviceName, serviceType) {
    this.init(name, priority, rate, reservoirSize,
              host, httpMethod, urlPath, serviceName, serviceType);
  }
docs: The data model for a sampling rule defined using X-Ray API CreateSamplingRules.
  It should be only instantiated directly from the X-Ray API response.
  @constructor