Oilpan: Prepare to move select and option elements to Oilpan heap.

Source/core/html/HTMLSelectElement.h

Index: Source/core/html/HTMLSelectElement.h
diff --git a/Source/core/html/HTMLSelectElement.h b/Source/core/html/HTMLSelectElement.h
index 926d22484b9ff3802f035fef1e4aabce135082f0..6b76380ae1631274cbcc2846c2bbe0cd18c5f8f4 100644
--- a/Source/core/html/HTMLSelectElement.h
+++ b/Source/core/html/HTMLSelectElement.h
@@ -82,7 +82,7 @@ public:
     void invalidateSelectedItems();
     void updateListItemSelectedStates();
 
-    const Vector<HTMLElement*>& listItems() const;
+    const WillBeHeapVector<RawPtrWillBeMember<HTMLElement> >& listItems() const;
 
     virtual void accessKeyAction(bool sendMouseEvents) OVERRIDE;
     void accessKeySetSelectedIndex(int);
@@ -114,9 +114,12 @@ public:
 
     // For use in the implementation of HTMLOptionElement.
     void optionSelectionStateChanged(HTMLOptionElement*, bool optionIsSelected);
-    bool anonymousIndexedSetter(unsigned, PassRefPtr<HTMLOptionElement>, ExceptionState&);
+    bool anonymousIndexedSetter(unsigned, PassRefPtrWillBeRawPtr<HTMLOptionElement>, ExceptionState&);
 
     void updateListOnRenderer();
+
+    virtual void trace(Visitor*) OVERRIDE;
+
 protected:
     HTMLSelectElement(Document&, HTMLFormElement*);
 
@@ -198,7 +201,7 @@ private:
     virtual String optionAtIndex(int index) const OVERRIDE;
 
     // m_listItems contains HTMLOptionElement, HTMLOptGroupElement, and HTMLHRElement objects.
-    mutable Vector<HTMLElement*> m_listItems;
+    mutable WillBeHeapVector<RawPtrWillBeMember<HTMLElement> > m_listItems;
     Vector<bool> m_lastOnChangeSelection;
     Vector<bool> m_cachedStateForActiveSelection;
     TypeAhead m_typeAhead;