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

Source/core/html/HTMLTextFormControlElement.h

Index: Source/core/html/HTMLTextFormControlElement.h
diff --git a/Source/core/html/HTMLTextFormControlElement.h b/Source/core/html/HTMLTextFormControlElement.h
index 506380be7c68275e8b4f99ddd090f386a2aa762d..5232cebfb4bc65efff3c83657236622299193cc2 100644
--- a/Source/core/html/HTMLTextFormControlElement.h
+++ b/Source/core/html/HTMLTextFormControlElement.h
@@ -90,6 +90,8 @@ public:
 
     virtual void reportMemoryUsage(MemoryObjectInfo*) const OVERRIDE;
 
+    virtual void acceptHeapVisitor(Visitor*) const OVERRIDE;
+
 protected:
     HTMLTextFormControlElement(const QualifiedName&, Document*, HTMLFormElement*);
     bool isPlaceholderEmpty() const;
@@ -147,13 +149,13 @@ inline bool isHTMLTextFormControlElement(const Node* node)
     return node->isElementNode() && toElement(node)->isTextFormControl();
 }
 
-inline HTMLTextFormControlElement* toHTMLTextFormControlElement(Node* node)
+inline Result<HTMLTextFormControlElement> toHTMLTextFormControlElement(Node* node)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!node || isHTMLTextFormControlElement(node));
-    return static_cast<HTMLTextFormControlElement*>(node);
+    return Handle<HTMLTextFormControlElement>(static_cast<HTMLTextFormControlElement*>(node));
 }
 
-HTMLTextFormControlElement* enclosingTextFormControl(const Position&);
+Result<HTMLTextFormControlElement> enclosingTextFormControl(const Position&);
 
 } // namespace