Only :host and :ancestor should ever match the host in a ShadowRoot

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 368 matching lines @@
     return m_match == PseudoElement && m_pseudoType == PseudoUnknown;
 }
 
 inline bool CSSSelector::isCustomPseudoElement() const
 {
     return m_match == PseudoElement && (m_pseudoType == PseudoUserAgentCustomElement || m_pseudoType == PseudoWebKitCustomElement);
 }
 
 inline bool CSSSelector::isHostPseudoClass() const
 {
-    return m_match == PseudoClass && m_pseudoType == PseudoHost;
+    return m_match == PseudoClass && (m_pseudoType == PseudoHost || m_pseudoType == PseudoAncestor);
 }
 
 inline bool CSSSelector::isSiblingSelector() const
 {
     PseudoType type = pseudoType();
     return m_relation == DirectAdjacent
         || m_relation == IndirectAdjacent
         || type == PseudoEmpty
         || type == PseudoFirstChild
         || type == PseudoFirstOfType
@@ skipping 114 matching lines @@
     if (m_hasRareData)
         return m_data.m_rareData->m_value;
     // 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);
 }
 
 } // namespace WebCore
 
 #endif // CSSSelector_h