anchor.diff:          : false);
     }
   
  -  void shimPolyfillUnscopedRule(RuleSet ruleSet) {
  +  void _shimPolyfillUnscopedRule(RuleSet ruleSet) {
       if (_matchesElement(ruleSet.selectorGroup, 'polyfill-unscoped-rule')) {
         var contentSelectorGroup = _selectorGroupForProperty(
             ruleSet.declarationGroup, 'content',
  
positive.code: 
  /// Shims selectors to emulate Shadow DOM CSS style encapsulation.
  class _ShadowTransformer extends Visitor {
    final String contentClass;
    final String hostClass;
  
    _ShadowTransformer(this.contentClass, this.hostClass);
  
    void visitTree(StyleSheet tree) {
      tree.visit(this);
    }
  
negative.code: 
    final _unscopedSelectorGroups = <SelectorGroup>{};
  
    void _shimPolyfillNextSelector(List<TreeNode> list) {
      SelectorGroup nextSelectorGroup;
  
      // Apply 'polyfill-next-selector' transformations.
  