Pseudo element selectors in compound selector lists are invalid.

third_party/WebKit/Source/core/css/parser/CSSParserSelector.h

 /*
  * Copyright (C) 2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 39 matching lines @@
     void setRelationIsAffectedByPseudoContent() { m_selector->setRelationIsAffectedByPseudoContent(); }
     bool relationIsAffectedByPseudoContent() const { return m_selector->relationIsAffectedByPseudoContent(); }
 
     void updatePseudoType(const AtomicString& value, bool hasArguments = false) const { m_selector->updatePseudoType(value, hasArguments); }
 
     void adoptSelectorVector(Vector<OwnPtr<CSSParserSelector>>& selectorVector);
     void setSelectorList(PassOwnPtr<CSSSelectorList>);
 
     bool hasHostPseudoSelector() const;
 
+    CSSSelector::Match match() const { return m_selector->match(); }
     CSSSelector::PseudoType pseudoType() const { return m_selector->pseudoType(); }
 
     // TODO(esprehn): This set of cases doesn't make sense, why PseudoShadow but not a check for ::content or /deep/ ?
     bool crossesTreeScopes() const { return pseudoType() == CSSSelector::PseudoWebKitCustomElement || pseudoType() == CSSSelector::PseudoCue || pseudoType() == CSSSelector::PseudoShadow; }
 
     bool isSimple() const;
     bool hasShadowPseudo() const;
 
     CSSParserSelector* tagHistory() const { return m_tagHistory.get(); }
     void setTagHistory(PassOwnPtr<CSSParserSelector> selector) { m_tagHistory = selector; }
     void clearTagHistory() { m_tagHistory.clear(); }
     void insertTagHistory(CSSSelector::Relation before, PassOwnPtr<CSSParserSelector>, CSSSelector::Relation after);
     void appendTagHistory(CSSSelector::Relation, PassOwnPtr<CSSParserSelector>);
     void prependTagSelector(const QualifiedName&, bool tagIsImplicit = false);
 
 private:
     OwnPtr<CSSSelector> m_selector;
     OwnPtr<CSSParserSelector> m_tagHistory;
 };
 
 inline bool CSSParserSelector::hasShadowPseudo() const
 {
     return m_selector->relation() == CSSSelector::ShadowPseudo;
 }
 
 } // namespace blink
 
 #endif