*
   * @since 15.0
   */
  public static Stopwatch createStarted(Ticker ticker) {
    return new Stopwatch(ticker).start();
  }

  Stopwatch() {
    this.ticker = Ticker.systemTicker();
  }

  Stopwatch(Ticker ticker) {
    this.ticker = checkNotNull(ticker, "ticker");
  }

  /**
   * Returns {@code true} if {@link #start()} has been called on this stopwatch, and {@link #stop()}