onStart_(event) {
    if (this.ws_.isDisabled()) {
      return;
    }

    const info = Touch.normalizeEventInfo(event);

    if (event.touches.length === 1) {
      this.startX_ = info.x;
      this.startY_ = info.y;
      this.endX_ = info.x;
      this.endY_ = info.y;
    } else if (event.touches.length > 1) {
      this.startTouches = Touch.getTouchCoordinates(event);
      this.endTouches = this.startTouches;
      this.isGesture = true;
    }
  }
Start touch handler. Saves starting points.
@param {Event} event The Touch event.
@private