Replace style sharing cousin list search with LRU

Source/core/css/resolver/StyleResolver.h

Index: Source/core/css/resolver/StyleResolver.h
diff --git a/Source/core/css/resolver/StyleResolver.h b/Source/core/css/resolver/StyleResolver.h
index 2a78cb7be7c4babb3ee4a4d7ecd6fcce08b3ac16..5d9ae8ebe4a90eed5355db76582b542602d0b903 100644
--- a/Source/core/css/resolver/StyleResolver.h
+++ b/Source/core/css/resolver/StyleResolver.h
@@ -36,6 +36,7 @@
 #include "core/css/resolver/StyleBuilder.h"
 #include "core/css/resolver/StyleResolverState.h"
 #include "core/css/resolver/StyleResourceLoader.h"
+#include "wtf/Deque.h"
 #include "wtf/HashMap.h"
 #include "wtf/HashSet.h"
 #include "wtf/RefPtr.h"
@@ -85,6 +86,9 @@ enum RuleMatchingBehavior {
     MatchOnlyUserAgentRules,
 };
 
+const unsigned styleSharingListSize = 40;
+typedef WTF::Deque<RefPtr<Element>, styleSharingListSize> StyleSharingList;
+
 #undef STYLE_STATS
 
 #ifdef STYLE_STATS
@@ -273,6 +277,13 @@ public:
 
     const RuleFeatureSet& ruleFeatureSet() const { return m_features; }
 
+    StyleSharingList& styleSharingList() { return m_styleSharingList; }
+
+    bool supportsStyleSharing(Element*);
+
+    void addToStyleSharingList(Element*);
+    void clearStyleSharingList();
+
 #ifdef STYLE_STATS
     ALWAYS_INLINE static StyleSharingStats& styleSharingStats() { return m_styleSharingStats; }
 #endif
@@ -356,6 +367,8 @@ private:
 
     StyleResourceLoader m_styleResourceLoader;
 
+    StyleSharingList m_styleSharingList;
+
 #ifdef STYLE_STATS
     static StyleSharingStats m_styleSharingStats;
 #endif