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

Source/core/dom/Node.cpp

Index: Source/core/dom/Node.cpp
diff --git a/Source/core/dom/Node.cpp b/Source/core/dom/Node.cpp
index b4f65e799e2b1abaef1ccf2166296f9779336ba7..4d0ab6bf92cc79124fdf7b6209875b485e7a9b02 100644
--- a/Source/core/dom/Node.cpp
+++ b/Source/core/dom/Node.cpp
@@ -486,13 +486,13 @@ Node* Node::toNode()
     return this;
 }
 
-HTMLInputElement* Node::toInputElement()
+Result<HTMLInputElement> Node::toInputElement()
 {
     // If one of the below ASSERTs trigger, you are calling this function
     // directly or indirectly from a constructor or destructor of this object.
     // Don't do this!
     ASSERT(!(isHTMLElement() && hasTagName(inputTag)));
-    return 0;
+    return nullptr;
 }
 
 short Node::tabIndex() const