Remove support for pseudo classes in <content select>.

Source/core/html/HTMLContentElement.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 49 matching lines @@
     bool isSelectValid() const;
 
 private:
     HTMLContentElement(Document&, PassOwnPtrWillBeRawPtr<HTMLContentSelectFilter>);
 
     virtual void parseAttribute(const QualifiedName&, const AtomicString&) override;
 
     bool validateSelect() const;
     void parseSelect();
 
-    bool matchSelector(const WillBeHeapVector<RawPtrWillBeMember<Node>, 32>& siblings, int nth) const;
+    bool matchSelector(Element&) const;
 
     bool m_shouldParseSelect;
     bool m_isValidSelector;
     AtomicString m_select;
     CSSSelectorList m_selectorList;
     OwnPtrWillBeMember<HTMLContentSelectFilter> m_filter;
 };
 
 inline const CSSSelectorList& HTMLContentElement::selectorList() const
 {
@@ skipping 12 matching lines @@
 inline bool HTMLContentElement::canSelectNode(const WillBeHeapVector<RawPtrWillBeMember<Node>, 32>& siblings, int nth) const
 {
     if (m_filter)
         return m_filter->canSelectNode(siblings, nth);
     if (m_select.isNull() || m_select.isEmpty())
         return true;
     if (!isSelectValid())
         return false;
     if (!siblings[nth]->isElementNode())
         return false;
-    return matchSelector(siblings, nth);
+    return matchSelector(*toElement(siblings[nth]));
 }
 
 } // namespace blink
 
 #endif // HTMLContentElement_h