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

Source/core/css/parser/BisonCSSParser-in.cpp

 /*
  * Copyright (C) 2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2012 Adobe Systems Incorporated. All rights reserved.
  * Copyright (C) 2012 Intel Corporation. All rights reserved.
  *
@@ skipping 1916 matching lines @@
     QualifiedName tag(namespacePrefix, elementName, determinedNamespace);
 
     if (CSSParserSelector* distributedPseudoElementSelector = specifiers->findDistributedPseudoElementSelector()) {
         specifiers->prependTagSelector(tag, tagIsForNamespaceRule);
         return rewriteSpecifiersForShadowDistributed(specifiers, distributedPseudoElementSelector);
     }
 
     if (specifiers->needsCrossingTreeScopeBoundary())
         return rewriteSpecifiersWithElementNameForCustomPseudoElement(tag, elementName, specifiers, tagIsForNamespaceRule);
 
-    if (tag == anyQName())
+    // *:host never matches, so we can't discard the * otherwise we can't tell the
+    // difference between *:host and just :host.
+    if (tag == anyQName() && !specifiers->hasHostPseudoSelector())
         return specifiers;
-    if (!(specifiers->pseudoType() == CSSSelector::PseudoCue))
+    if (specifiers->pseudoType() != CSSSelector::PseudoCue)
         specifiers->prependTagSelector(tag, tagIsForNamespaceRule);
     return specifiers;
 }
 
 CSSParserSelector* BisonCSSParser::rewriteSpecifiersWithElementNameForCustomPseudoElement(const QualifiedName& tag, const AtomicString& elementName, CSSParserSelector* specifiers, bool tagIsForNamespaceRule)
 {
     if (m_context.useCounter() && specifiers->pseudoType() == CSSSelector::PseudoUserAgentCustomElement)
         m_context.useCounter()->count(UseCounter::CSSPseudoElementUserAgentCustomPseudo);
 
     CSSParserSelector* lastShadowPseudo = specifiers;
@@ skipping 255 matching lines @@
     rule->setProperties(createStylePropertySet());
     clearProperties();
 
     StyleRuleViewport* result = rule.get();
     m_parsedRules.append(rule.release());
 
     return result;
 }
 
 }