Method tick

src/service/performance-impl.js:799–835

* Ticks a timing event. * * @param {TickLabel_Enum} label The variable name as it will be reported. * See TICKEVENTS.md for available metrics, and edit this file * when adding a new metric. * @param {number=} opt_delta The delta. Call tickDelta instead of setting * this

(label, opt_delta, opt_value)

   * @param {number=} opt_value The value to use. Overrides default calculation.
   */
  tick(label, opt_delta, opt_value) {
    devAssert(
      opt_delta == undefined || opt_value == undefined,
      'You may not set both opt_delta and opt_value.'
    );

    const data = {'label': label};
    let delta;

    if (opt_delta != undefined) {
      data['delta'] = delta = Math.max(opt_delta, 0);
    } else if (opt_value != undefined) {
      data['value'] = opt_value;
    } else {
      // Marking only makes sense for non-overridden values (and no deltas).
      this.mark(label);
      delta = this.win.performance.now();
      data['value'] = this.timeOrigin_ + delta;
    }

    // Emit events. Used by `amp performance`.
    this.win.dispatchEvent(
      createCustomEvent(
        this.win,
        'perf',
        /** @type {JsonObject} */ ({label, delta})
      )
    );

    if (this.isMessagingReady_ && this.isPerformanceTrackingOn_) {
      this.viewer_.sendMessage('tick', data);
    } else {
      this.queueTick_(data);
    }

    this.metrics_.signal(label, delta);
  }

  /**
   * Add browser performance timeline entries for simple ticks.