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

Source/core/css/resolver/ScopedStyleTree.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.
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 37 matching lines @@
 
     ScopedStyleResolver* scopedStyleResolverFor(const ContainerNode& scopingNode);
     ScopedStyleResolver* addScopedStyleResolver(ContainerNode& scopingNode, bool& isNewEntry);
     void clear();
 
     // for fast-path.
     bool hasOnlyScopedResolverForDocument() const { return m_scopedResolverForDocument && m_authorStyles.size() == 1; }
     ScopedStyleResolver* scopedStyleResolverForDocument() const { return m_scopedResolverForDocument; }
 
     void resolveScopedStyles(const Element*, Vector<ScopedStyleResolver*, 8>&);
-    void collectScopedResolversForHostedShadowTrees(const Element*, Vector<ScopedStyleResolver*, 8>&);
     void resolveScopedKeyframesRules(const Element*, Vector<ScopedStyleResolver*, 8>&);
-    ScopedStyleResolver* scopedResolverFor(const Element*);
+    ScopedStyleResolver* scopedResolverFor(const ContainerNode*);
 
     void remove(const ContainerNode* scopingNode);
 
     void pushStyleCache(const ContainerNode& scopingNode, const ContainerNode* parent);
     void popStyleCache(const ContainerNode& scopingNode);
 
     void collectFeaturesTo(RuleFeatureSet& features);
     void setBuildInDocumentOrder(bool enabled) { m_buildInDocumentOrder = enabled; }
     bool buildInDocumentOrder() const { return m_buildInDocumentOrder; }
 
 private:
+    ContainerNode* traverseParent(const ContainerNode*) const;
     void setupScopedStylesTree(ScopedStyleResolver* target);
 
     bool cacheIsValid(const ContainerNode* parent) const { return parent && parent == m_cache.nodeForScopedStyles; }
     void resolveStyleCache(const ContainerNode* scopingNode);
     ScopedStyleResolver* enclosingScopedStyleResolverFor(const ContainerNode* scopingNode);
 
     void reparentNodes(const ScopedStyleResolver* oldParent, ScopedStyleResolver* newParent);
 
 private:
     HashMap<const ContainerNode*, OwnPtr<ScopedStyleResolver> > m_authorStyles;
     ScopedStyleResolver* m_scopedResolverForDocument;
     bool m_buildInDocumentOrder;
 
     struct ScopedStyleCache {
         ScopedStyleResolver* scopedResolver;
         const ContainerNode* nodeForScopedStyles;
 
         void clear()
         {
             scopedResolver = 0;
             nodeForScopedStyles = 0;
         }
     };
     ScopedStyleCache m_cache;
 };
 
-inline ScopedStyleResolver* ScopedStyleTree::scopedResolverFor(const Element* element)
+inline ScopedStyleResolver* ScopedStyleTree::scopedResolverFor(const ContainerNode* node)
 {
-    if (!cacheIsValid(element))
-        resolveStyleCache(element);
+    if (!cacheIsValid(node))
+        resolveStyleCache(node);
 
     return m_cache.scopedResolver;
 }
 
 } // namespace WebCore
 
 #endif // ScopedStyleTree_h