 = [];
        this._unlockedElementCache = [];
      },

      /**
       * Remove an element from the scroll lock stack. The element being
       * removed does not need to be the most recently pushed element. However,
       * the scroll lock constraints only change when the most recently pushed
       * element is removed.
       *
       * @param {HTMLElement} element The element to remove from the scroll
       * lock stack.
       */
      removeScrollLock: function(element) {
        var index = thi