code: function CounterSample(series, timestamp, value) {
      tr.model.Event.call(this);
      this.series_ = series;
      this.timestamp_ = timestamp;
      this.value_ = value;
    }
docs: The value of a given measurement at a given time.
  
  As an example, if we're measuring the throughput of data sent over a USB
  connection, each counter sample might represent the instantaneous
  throughput of the connection at a given time.
  
  @constructor
  @extends {Event}