domReplaceScope(node, oldScope, newScope) {
    const fn = (node) => {
      this.element(node, oldScope, true);
      this.element(node, newScope);
    };
    this._transformDom(node, fn);
  }
Given a node, replace the scoping class to each subnode in the tree.
@param {!Node} node
@param {string} oldScope
@param {string} newScope