showBackCornerButton(duration) {
    if (duration == null) { duration = 0.0; }

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

      this.removeBackNodes(duration);

      this.backNode = new BaseSprite(RSX.button_back_corner.img);
      this.backNode.setAnchorPoint(0.0, 1.0);
      this.addChild(this.backNode, this.backZOrder);

      // add as interactive
      this.addInteractiveElement(this.backNode);

      if (this.isRunning()) {
        // resize when this is already running (in scene)
        // otherwise, resize will occur automatically on first init
        this.resizeBackNodes();
      }

      if (duration != null && duration > 0.0) {
        this.backNode.setOpacity(0.0);
        this.backNode.fadeTo(duration, 255.0);
      }
    });
  }
Shows a back corner button.
@param {Number} [duration=0.0]
@returns {Promise}