function InertNode(node, inertRoot) {
      _classCallCheck(this, InertNode);

      /** @type {!Node} */
      this._node = node;

      /** @type {boolean} */
      this._overrodeFocusMethod = false;

      /**
       * @type {!Set<!InertRoot>} The set of descendant inert roots.
       *    If and only if this set becomes empty, this node is no longer inert.
       */
      this._inertRoots = new Set([inertRoot]);

      /** @type {?number} */
      this._savedTabIndex = null;

      /** @type {boolean} */
      this._destroyed = false;

      // Save any prior tabindex info and make this node untabbable
      this.ensureUntabbable();
    }
@param {!Node} node A focusable element to be made inert.
@param {!InertRoot} inertRoot The inert root element associated with this inert node.