dom(node, scope, shouldRemoveScope) {
    const fn = (node) => {
      this.element(node, scope || '', shouldRemoveScope);
    };
    this._transformDom(node, fn);
  }
Given a node and scope name, add a scoping class to each node
in the tree. This facilitates transforming css into scoped rules.
@param {!Node} node
@param {string} scope
@param {boolean=} shouldRemoveScope
@deprecated