Selectors in styles in shadowRoots should match in all of the host's shadowRoots.

Source/core/css/resolver/StyleResolver.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 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 233 matching lines @@
 
     void collectPseudoRulesForElement(Element*, ElementRuleCollector&, PseudoId, unsigned rulesToInclude);
     void matchUARules(ElementRuleCollector&, RuleSet*);
     void matchAuthorRules(Element*, ElementRuleCollector&, bool includeEmptyRules);
     void matchAuthorRulesForShadowHost(Element*, ElementRuleCollector&, bool includeEmptyRules, Vector<ScopedStyleResolver*, 8>& resolvers, Vector<ScopedStyleResolver*, 8>& resolversInShadowTree);
     void matchAllRules(StyleResolverState&, ElementRuleCollector&, bool includeSMILProperties);
     void matchUARules(ElementRuleCollector&);
     // FIXME: watched selectors should be implemented using injected author stylesheets: http://crbug.com/316960
     void matchWatchSelectorRules(ElementRuleCollector&);
     void collectFeatures();
-    void collectTreeBoundaryCrossingRules(Element*, ElementRuleCollector&, bool includeEmptyRules);
+    void collectTreeBoundaryCrossingRules(Element*, ElementRuleCollector&, bool includeEmptyRules, CascadeOrder);
     void resetRuleFeatures();
 
     bool fastRejectSelector(const RuleData&) const;
 
     void applyMatchedProperties(StyleResolverState&, const MatchResult&);
     void applyAnimatedProperties(StyleResolverState&, Element* animatingElement);
 
     enum StyleApplicationPass {
         VariableDefinitions,
         AnimationProperties,
@@ skipping 77 matching lines @@
         SelectorChecker::SelectorCheckingContext selectorCheckingContext(s, regionElement, SelectorChecker::VisitedMatchDisabled);
         if (selectorChecker.match(selectorCheckingContext, DOMSiblingTraversalStrategy()) == SelectorChecker::SelectorMatches)
             return true;
     }
     return false;
 }
 
 } // namespace WebCore
 
 #endif // StyleResolver_h