Remove support for pseudo classes in <content select>.

Source/core/html/HTMLContentElement.h

Index: Source/core/html/HTMLContentElement.h
diff --git a/Source/core/html/HTMLContentElement.h b/Source/core/html/HTMLContentElement.h
index 5ed3b18bdaa77cd19517403da0863fe4c15ff212..076974338d757b138c5ea16fdf49fa9aeeb96ea6 100644
--- a/Source/core/html/HTMLContentElement.h
+++ b/Source/core/html/HTMLContentElement.h
@@ -67,7 +67,7 @@ private:
     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;
@@ -100,7 +100,7 @@ inline bool HTMLContentElement::canSelectNode(const WillBeHeapVector<RawPtrWillB
         return false;
     if (!siblings[nth]->isElementNode())
         return false;
-    return matchSelector(siblings, nth);
+    return matchSelector(*toElement(siblings[nth]));
 }
 
 } // namespace blink