Consider pseudo classes as matching for shared style rejection.

third_party/WebKit/Source/core/css/CSSSelector.h

 /*
  * Copyright (C) 1999-2003 Lars Knoll (knoll@kde.org)
  *               1999 Waldo Bastian (bastian@kde.org)
  * Copyright (C) 2004, 2006, 2007, 2008, 2009, 2010, 2013 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.
  *
@@ skipping 242 matching lines @@
     void setArgument(const AtomicString&);
     void setSelectorList(std::unique_ptr<CSSSelectorList>);
 
     void setNth(int a, int b);
     bool matchNth(int count) const;
 
     bool isAdjacentSelector() const { return m_relation == DirectAdjacent || m_relation == IndirectAdjacent; }
     bool isShadowSelector() const { return m_relation == ShadowPseudo || m_relation == ShadowDeep; }
     bool isAttributeSelector() const { return m_match >= FirstAttributeSelectorMatch; }
     bool isHostPseudoClass() const { return m_pseudoType == PseudoHost || m_pseudoType == PseudoHostContext; }
+    bool isUserActionPseudoClass() const;
     bool isInsertionPointCrossing() const { return m_pseudoType == PseudoHostContext || m_pseudoType == PseudoContent; }
 
     RelationType relation() const { return static_cast<RelationType>(m_relation); }
     void setRelation(RelationType relation)
     {
         m_relation = relation;
         ASSERT(static_cast<RelationType>(m_relation) == relation); // using a bitfield.
     }
 
     MatchType match() const { return static_cast<MatchType>(m_match); }
@@ skipping 203 matching lines @@
 inline const AtomicString& CSSSelector::serializingValue() const
 {
     ASSERT(m_match != Tag);
     if (m_hasRareData)
         return m_data.m_rareData->m_serializingValue;
     // AtomicString is really just a StringImpl* so the cast below is safe.
     // FIXME: Perhaps call sites could be changed to accept StringImpl?
     return *reinterpret_cast<const AtomicString*>(&m_data.m_value);
 }
 
+inline bool CSSSelector::isUserActionPseudoClass() const
+{
+    return m_pseudoType == PseudoHover
+        || m_pseudoType == PseudoActive
+        || m_pseudoType == PseudoFocus
+        || m_pseudoType == PseudoDrag;
+}
+
 } // namespace blink
 
 #endif // CSSSelector_h