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

Source/core/html/HTMLFieldSetElement.cpp

Index: Source/core/html/HTMLFieldSetElement.cpp
diff --git a/Source/core/html/HTMLFieldSetElement.cpp b/Source/core/html/HTMLFieldSetElement.cpp
index d441041217c29d78515751eb4d0bf92de1af230c..9691fdd0420770a7c1fb545c7bba3d41c2073201 100644
--- a/Source/core/html/HTMLFieldSetElement.cpp
+++ b/Source/core/html/HTMLFieldSetElement.cpp
@@ -45,9 +45,9 @@ inline HTMLFieldSetElement::HTMLFieldSetElement(const QualifiedName& tagName, Do
     ScriptWrappable::init(this);
 }
 
-PassRefPtr<HTMLFieldSetElement> HTMLFieldSetElement::create(const QualifiedName& tagName, Document* document, HTMLFormElement* form)
+Result<HTMLFieldSetElement> HTMLFieldSetElement::create(const QualifiedName& tagName, Document* document, HTMLFormElement* form)
 {
-    return adoptRef(new HTMLFieldSetElement(tagName, document, form));
+    return adoptNode(new HTMLFieldSetElement(tagName, document, form));
 }
 
 void HTMLFieldSetElement::invalidateDisabledStateUnder(Element* base)
@@ -143,4 +143,9 @@ unsigned HTMLFieldSetElement::length() const
     return len;
 }
 
+void HTMLFieldSetElement::acceptHeapVisitor(Visitor* visitor) const
+{
+    HTMLFormControlElement::acceptHeapVisitor(visitor);
+}
+
 } // namespace