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

Source/core/html/HTMLLegendElement.cpp

Index: Source/core/html/HTMLLegendElement.cpp
diff --git a/Source/core/html/HTMLLegendElement.cpp b/Source/core/html/HTMLLegendElement.cpp
index 15e8b1ddd9dedc7242b52d8e1926992ec5848b2d..aad2cccb68cd3a8f48f4984c8758908195debca7 100644
--- a/Source/core/html/HTMLLegendElement.cpp
+++ b/Source/core/html/HTMLLegendElement.cpp
@@ -48,24 +48,24 @@ PassRefPtr<HTMLLegendElement> HTMLLegendElement::create(const QualifiedName& tag
     return adoptRef(new HTMLLegendElement(tagName, document));
 }
 
-HTMLFormControlElement* HTMLLegendElement::associatedControl()
+Result<HTMLFormControlElement> HTMLLegendElement::associatedControl()
 {
     // Check if there's a fieldset belonging to this legend.
     Element* fieldset = parentElement();
     while (fieldset && !fieldset->hasTagName(fieldsetTag))
         fieldset = fieldset->parentElement();
     if (!fieldset)
-        return 0;
+        return nullptr;
 
     // Find first form element inside the fieldset that is not a legend element.
     // FIXME: Should we consider tabindex?
     Element* element = fieldset;
     while ((element = ElementTraversal::next(element, fieldset))) {
         if (element->isFormControlElement())
-            return static_cast<HTMLFormControlElement*>(element);
+            return Handle<HTMLFormControlElement>(static_cast<HTMLFormControlElement*>(element));
     }
 
-    return 0;
+    return nullptr;
 }
 
 void HTMLLegendElement::focus(bool, FocusDirection direction)
@@ -74,13 +74,13 @@ void HTMLLegendElement::focus(bool, FocusDirection direction)
         Element::focus(true, direction);
         
     // To match other browsers' behavior, never restore previous selection.
-    if (HTMLFormControlElement* control = associatedControl())
+    if (Handle<HTMLFormControlElement> control = associatedControl())
         control->focus(false, direction);
 }
 
 void HTMLLegendElement::accessKeyAction(bool sendMouseEvents)
 {
-    if (HTMLFormControlElement* control = associatedControl())
+    if (Handle<HTMLFormControlElement> control = associatedControl())
         control->accessKeyAction(sendMouseEvents);
 }