showGlow(duration, color) {
    if (!this._isGlowing) {
      this._isGlowing = true;

      return this.whenRequiredResourcesReady().then((requestId) => {
        if (!this.getAreResourcesValid(requestId)) return; // load invalidated or resources changed

        if (this._glowImageMap == null) {
          this._glowImageMap = FXGlowImageMap.create(this._getLootCrateGlowSpriteIdentifier());
          this._lootCrateContainerNode.addChild(this._glowImageMap, -1);
        }

        if (duration == null) {
          duration = 0.0;
        }
        if (color == null) {
          color = CONFIG.LOOT_CRATE_GLOW_COLOR;
        }
        this._glowImageMap.setGlowColor(color);
        this._glowImageMap.fadeTo(duration, 255.0);
      });
    }
  }
Shows the loot crate as glowing.
@param {Number} [duration=0.0]
@param {cc.Color} [color=CONFIG.LOOT_CRATE_GLOW_COLOR]
@public
@return {Promise}