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

Source/core/rendering/RenderTextControlSingleLine.cpp

Index: Source/core/rendering/RenderTextControlSingleLine.cpp
diff --git a/Source/core/rendering/RenderTextControlSingleLine.cpp b/Source/core/rendering/RenderTextControlSingleLine.cpp
index 86bc8ee5ec0afc97f6f58704343cc853e50a05a9..13bee7de9e2d5843e085fd4f03f8b22677fad8f7 100644
--- a/Source/core/rendering/RenderTextControlSingleLine.cpp
+++ b/Source/core/rendering/RenderTextControlSingleLine.cpp
@@ -475,7 +475,7 @@ bool RenderTextControlSingleLine::logicalScroll(ScrollLogicalDirection direction
     return RenderBlock::logicalScroll(direction, granularity, multiplier, stopNode);
 }
 
-HTMLInputElement* RenderTextControlSingleLine::inputElement() const
+Result<HTMLInputElement> RenderTextControlSingleLine::inputElement() const
 {
     return node()->toInputElement();
 }