[oilpan] Completely move HTMLFormControlElement's hierarchy to the managed heap

Source/core/page/DragController.h

Index: Source/core/page/DragController.h
diff --git a/Source/core/page/DragController.h b/Source/core/page/DragController.h
index ecd0a3d8081cb1873574af848f6c22532ea35b1a..6b3e35d09b5cdbc0ee551c82a55be2384a492e16 100644
--- a/Source/core/page/DragController.h
+++ b/Source/core/page/DragController.h
@@ -30,6 +30,7 @@
 #include "core/platform/DragImage.h"
 #include "core/platform/KURL.h"
 #include "core/platform/graphics/IntPoint.h"
+#include "heap/Handle.h"
 
 namespace WebCore {
 
@@ -120,7 +121,7 @@ namespace WebCore {
 
         RefPtr<Document> m_documentUnderMouse; // The document the mouse was last dragged over.
         RefPtr<Document> m_dragInitiator; // The Document (if any) that initiated the drag.
-        RefPtr<HTMLInputElement> m_fileInputElementUnderMouse;
+        Persistent<HTMLInputElement> m_fileInputElementUnderMouse;
         bool m_documentIsHandlingDrag;
 
         DragDestinationAction m_dragDestinationAction;