Avoid style sharing with mis-matched descendant selectors

Source/core/css/resolver/SharedStyleFinder.h

 /*
  * Copyright (C) 2013 Google, Inc.
  * 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.
  *
@@ skipping 20 matching lines @@
 class RuleFeatureSet;
 class RuleSet;
 class SpaceSplitString;
 class StyleResolver;
 
 class SharedStyleFinder {
 public:
     // RuleSets are passed non-const as the act of matching against them can cause them
     // to be compacted. :(
     SharedStyleFinder(const RuleFeatureSet& features, RuleSet* siblingRuleSet,
-        RuleSet* uncommonAttributeRuleSet, StyleResolver* styleResolver)
+        RuleSet* uncommonAttributeRuleSet, RuleSet* descendantRuleSet, StyleResolver* styleResolver)
         : m_elementAffectedByClassRules(false)
         , m_features(features)
         , m_siblingRuleSet(siblingRuleSet)
         , m_uncommonAttributeRuleSet(uncommonAttributeRuleSet)
+        , m_descendantRuleSet(descendantRuleSet)
         , m_styleResolver(styleResolver)
     { }
 
     // FIXME: It is not necessarily safe to call this method more than once.
     RenderStyle* locateSharedStyle(const ElementResolveContext&);
 
 private:
     Element* findElementForStyleSharing(const ElementResolveContext&) const;
 
     // Only used when we're collecting stats on styles
     Element* searchDocumentForSharedStyle(const ElementResolveContext&) const;
 
     bool classNamesAffectedByRules(const SpaceSplitString&) const;
 
     bool canShareStyleWithElement(const ElementResolveContext&, Element*) const;
     bool canShareStyleWithControl(const ElementResolveContext&, Element*) const;
     bool sharingCandidateHasIdenticalStyleAffectingAttributes(const ElementResolveContext&, Element*) const;
     bool matchesRuleSet(const ElementResolveContext&, RuleSet*);
+    bool candidateMatchesDescendantRules(const ElementResolveContext&, Element*) const;
 
     bool m_elementAffectedByClassRules;
     const RuleFeatureSet& m_features;
     RuleSet* m_siblingRuleSet;
     RuleSet* m_uncommonAttributeRuleSet;
+    RuleSet* m_descendantRuleSet;
     StyleResolver* m_styleResolver;
 };
 
 } // namespace WebCore
 
 #endif // SharedStyleFinder_h