Lazily generate HistoryItem's serialized form state

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 43eed37802f11bb64303564d80c286855c259bd0..6a79f71e4055664c28055d3f814bf7d303c2860f 100644
--- a/Source/core/dom/Document.h
+++ b/Source/core/dom/Document.h
@@ -88,6 +88,7 @@ class DocumentLifecycleObserver;
 class DocumentLoader;
 class DocumentMarkerController;
 class DocumentParser;
+class DocumentState;
 class DocumentTimeline;
 class DocumentType;
 class Element;
@@ -456,7 +457,7 @@ public:
     void evaluateMediaQueryList();
 
     FormController& formController();
-    Vector<String> formElementsState() const;
+    DocumentState* formElementsState() const;
     void setStateForNewFormElements(const Vector<String>&);
 
     FrameView* view() const; // can be null
@@ -610,9 +611,6 @@ public:
     void setParsing(bool);
     bool parsing() const { return m_isParsing; }
 
-    void setHistoryItemDocumentStateDirty(bool dirty) { m_historyItemDocumentStateDirty = dirty; }
-    bool historyItemDocumentStateDirty() const { return m_historyItemDocumentStateDirty; }
-
     bool shouldScheduleLayout() const;
     int elapsedTime() const;
 
@@ -1243,7 +1241,6 @@ private:
     bool m_visuallyOrdered;
     ReadyState m_readyState;
     bool m_isParsing;
-    bool m_historyItemDocumentStateDirty;
 
     bool m_gotoAnchorNeededAfterStylesheetsLoad;
     bool m_isDNSPrefetchEnabled;