Cache element indices for :nth-child and :nth-last-child selectors.

Source/core/dom/Document.h

Index: Source/core/dom/Document.h
diff --git a/Source/core/dom/Document.h b/Source/core/dom/Document.h
index 51a3c60befaffd8c8722eedee272a4a7ce04c092..bf14e6dbb835fbc03e33beceabca0fa03b59cbdb 100644
--- a/Source/core/dom/Document.h
+++ b/Source/core/dom/Document.h
@@ -128,6 +128,7 @@ class MediaQueryListListener;
 class MediaQueryMatcher;
 class NodeFilter;
 class NodeIterator;
+class NthIndexCache;
 class Page;
 class PlatformMouseEvent;
 class ProcessingInstruction;
@@ -247,6 +248,7 @@ public:
     virtual bool canContainRangeEndPoint() const override { return true; }
 
     SelectorQueryCache& selectorQueryCache();
+    NthIndexCache* nthIndexCache();
 
     // Focus Management.
     Element* activeElement() const;
@@ -1061,6 +1063,25 @@ public:
 
     OriginsUsingFeatures::Value& originsUsingFeaturesValue() { return m_originsUsingFeaturesValue; }
 
+    class UseNthIndexCacheScope {
+        STACK_ALLOCATED();
+        WTF_MAKE_NONCOPYABLE(UseNthIndexCacheScope);
+    public:
+        UseNthIndexCacheScope(Document& document)
+            : m_document(&document)
+        {
+            ASSERT(!document.useNthIndexCache());
+            document.setUseNthIndexCache(true);
+        }
+        ~UseNthIndexCacheScope()
+        {
+            ASSERT(m_document->useNthIndexCache());
+            m_document->setUseNthIndexCache(false);
+        }
+    private:
+        RawPtrWillBeMember<Document> m_document;
+    };
+
 protected:
     Document(const DocumentInit&, DocumentClassFlags = DefaultDocumentClass);
 
@@ -1317,6 +1338,7 @@ private:
     WillBeHeapHashMap<String, RefPtrWillBeMember<HTMLCanvasElement>> m_cssCanvasElements;
 
     OwnPtr<SelectorQueryCache> m_selectorQueryCache;
+    OwnPtrWillBeMember<NthIndexCache> m_nthIndexCache;
 
     bool m_useSecureKeyboardEntryWhenActive;
 
@@ -1397,6 +1419,11 @@ private:
     ParserSynchronizationPolicy m_parserSyncPolicy;
 
     OriginsUsingFeatures::Value m_originsUsingFeaturesValue;
+
+    bool useNthIndexCache() const { return m_useNthIndexCache; }

[sof, 2015/03/30 13:27:53]

Let's move up the accessors, away from the field declarations.

[rune, 2015/03/30 20:14:40]

Done.

+    void setUseNthIndexCache(bool);
+
+    bool m_useNthIndexCache;
 };
 
 inline bool Document::shouldOverrideLegacyDescription(ViewportDescription::Type origin)