Lazily generate HistoryItem's serialized form state

Source/core/html/forms/FormController.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2010, 2011, 2012 Google 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 53 matching lines @@
     m_values = another.m_values;
     return *this;
 }
 
 inline void FormControlState::append(const String& value)
 {
     m_type = TypeRestore;
     m_values.append(value);
 }
 
+typedef HashMap<AtomicString, OwnPtr<SavedFormState> > SavedFormStateMap;
+
+class DocumentState : public RefCounted<DocumentState> {
+public:
+    static PassRefPtr<DocumentState> create();
+    ~DocumentState();
+
+    void addControl(HTMLFormControlElementWithState*);
+    void removeControl(HTMLFormControlElementWithState*);
+    Vector<String> toStateVector();
+
+private:
+    typedef ListHashSet<RefPtr<HTMLFormControlElementWithState>, 64> FormElementListHashSet;
+    FormElementListHashSet m_formControls;
+};
+
 class FormController {
     WTF_MAKE_FAST_ALLOCATED;
 public:
     static PassOwnPtr<FormController> create()
     {
         return adoptPtr(new FormController);
     }
     ~FormController();
 
     RadioButtonGroupScope& radioButtonGroupScope() { return m_radioButtonGroupScope; }
 
     void registerStatefulFormControl(HTMLFormControlElementWithState&);
     void unregisterStatefulFormControl(HTMLFormControlElementWithState&);
     // This should be callled only by Document::formElementsState().
-    Vector<String> formElementsState() const;
+    DocumentState* formElementsState() const;
     // This should be callled only by Document::setStateForNewFormElements().
     void setStateForNewFormElements(const Vector<String>&);
     void willDeleteForm(HTMLFormElement*);
     void restoreControlStateFor(HTMLFormControlElementWithState&);
     void restoreControlStateIn(HTMLFormElement&);
 
     static Vector<String> getReferencedFilePaths(const Vector<String>& stateVector);
 
 private:
-    typedef ListHashSet<RefPtr<HTMLFormControlElementWithState>, 64> FormElementListHashSet;
-    typedef HashMap<AtomicString, OwnPtr<SavedFormState> > SavedFormStateMap;
-
     FormController();
-    static PassOwnPtr<SavedFormStateMap> createSavedFormStateMap(const FormElementListHashSet&);
     FormControlState takeStateForFormElement(const HTMLFormControlElementWithState&);
     static void formStatesFromStateVector(const Vector<String>&, SavedFormStateMap&);
 
     RadioButtonGroupScope m_radioButtonGroupScope;
-    FormElementListHashSet m_formControls;
+    RefPtr<DocumentState> m_documentState;
     SavedFormStateMap m_savedFormStateMap;
     OwnPtr<FormKeyGenerator> m_formKeyGenerator;
 };
 
 } // namespace WebCore
 #endif