Replace RenderArena with PartitionAlloc.

Source/core/rendering/RenderWidgetProtector.h

Index: Source/core/rendering/RenderWidgetProtector.h
diff --git a/Source/core/rendering/RenderWidgetProtector.h b/Source/core/rendering/RenderWidgetProtector.h
index 2a65ab4393508eb301e119b05f1bf4fc51d80b1a..79ac031158e044388a8b28dfb31f7cabafcb9f00 100644
--- a/Source/core/rendering/RenderWidgetProtector.h
+++ b/Source/core/rendering/RenderWidgetProtector.h
@@ -35,18 +35,17 @@ class RenderWidgetProtector {
 public:
     explicit RenderWidgetProtector(RenderWidget* object)
         : m_object(object)
-        , m_arena(object->ref())
     {
+        m_object->ref();
     }
 
     ~RenderWidgetProtector()
     {
-        m_object->deref(m_arena);
+        m_object->deref();
     }
 
 private:
     RenderWidget* m_object;
-    RenderArena* m_arena;
 };
 
 }