sample(
      durationMs, numBytes) {
    if (numBytes < this.minBytes_) {
      return;
    }

    const bandwidth = 8000 * numBytes / durationMs;
    const weight = durationMs / 1000;

    this.bytesSampled_ += numBytes;
    this.fast_.sample(weight, bandwidth);
    this.slow_.sample(weight, bandwidth);
  }
Takes a bandwidth sample.

@param {number} durationMs The amount of time, in milliseconds, for a
  particular request.
@param {number} numBytes The total number of bytes transferred in that
  request.