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

Source/core/html/HTMLOutputElement.h

Index: Source/core/html/HTMLOutputElement.h
diff --git a/Source/core/html/HTMLOutputElement.h b/Source/core/html/HTMLOutputElement.h
index 0d48523878ef742282c758b0a33b78de78981f5f..155c4630c6019f61c45bcba44bb61c3ffa7c73ee 100644
--- a/Source/core/html/HTMLOutputElement.h
+++ b/Source/core/html/HTMLOutputElement.h
@@ -39,7 +39,7 @@ namespace WebCore {
 
 class HTMLOutputElement : public HTMLFormControlElement {
 public:
-    static PassRefPtr<HTMLOutputElement> create(const QualifiedName&, Document*, HTMLFormElement*);
+    static Result<HTMLOutputElement> create(const QualifiedName&, Document*, HTMLFormElement*);
 
     virtual bool willValidate() const { return false; }
 
@@ -52,6 +52,8 @@ public:
     
     virtual bool canContainRangeEndPoint() const { return false; }
 
+    virtual void acceptHeapVisitor(Visitor*) const OVERRIDE;
+
 private:
     HTMLOutputElement(const QualifiedName&, Document*, HTMLFormElement*);