Move member function rootEditableElement() out from VisiblePosition class

Source/core/editing/VisiblePosition.h

Index: Source/core/editing/VisiblePosition.h
diff --git a/Source/core/editing/VisiblePosition.h b/Source/core/editing/VisiblePosition.h
index 02a389e7b9bcc1f3855196c51c0d176866de4674..fec1dd6a39144551dfe3446798f3e48067d0035f 100644
--- a/Source/core/editing/VisiblePosition.h
+++ b/Source/core/editing/VisiblePosition.h
@@ -93,9 +93,6 @@ public:
     PositionWithAffinity toPositionWithAffinity() const { return PositionWithAffinity(m_deepPosition, m_affinity); }
     TextAffinity affinity() const { return m_affinity; }
 
-    // TODO(yosin) This does not handle [table, 0] correctly.
-    Element* rootEditableElement() const { return m_deepPosition.isNotNull() ? m_deepPosition.anchorNode()->rootEditableElement() : 0; }
-
     DECLARE_TRACE();
 
 #ifndef NDEBUG