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

Source/core/html/HTMLButtonElement.cpp

Index: Source/core/html/HTMLButtonElement.cpp
diff --git a/Source/core/html/HTMLButtonElement.cpp b/Source/core/html/HTMLButtonElement.cpp
index 82a44dd397a996ceb067466c421411278c9fa9a8..5fa87430d87bdc221dcea38666b1ed950b28f8e6 100644
--- a/Source/core/html/HTMLButtonElement.cpp
+++ b/Source/core/html/HTMLButtonElement.cpp
@@ -49,9 +49,9 @@ inline HTMLButtonElement::HTMLButtonElement(const QualifiedName& tagName, Docume
     ScriptWrappable::init(this);
 }
 
-PassRefPtr<HTMLButtonElement> HTMLButtonElement::create(const QualifiedName& tagName, Document* document, HTMLFormElement* form)
+Result<HTMLButtonElement> HTMLButtonElement::create(const QualifiedName& tagName, Document* document, HTMLFormElement* form)
 {
-    return adoptRef(new HTMLButtonElement(tagName, document, form));
+    return adoptNode(new HTMLButtonElement(tagName, document, form));
 }
 
 void HTMLButtonElement::setType(const AtomicString& type)
@@ -208,4 +208,9 @@ bool HTMLButtonElement::recalcWillValidate() const
     return m_type == SUBMIT && HTMLFormControlElement::recalcWillValidate();
 }
 
+void HTMLButtonElement::acceptHeapVisitor(Visitor* visitor) const
+{
+    HTMLFormControlElement::acceptHeapVisitor(visitor);
+}
+
 } // namespace