Get rid of unused member function rootEditableElement() in PositionAlgorithm<Strategy> template clas

Source/core/editing/Position.h

 /*
  * Copyright (C) 2004, 2006, 2008 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 142 matching lines @@
     // iterator. This position must be a |PositionAnchorType::OffsetInAhcor| to
     // behave as |Range| boundary point.
     Node* nodeAsRangePastLastNode() const;
 
     Node* commonAncestorContainer(const PositionAlgorithm<Strategy>&) const;
 
     Node* anchorNode() const { return m_anchorNode.get(); }
 
     Document* document() const { return m_anchorNode ? &m_anchorNode->document() : 0; }
     bool inDocument() const { return m_anchorNode && m_anchorNode->inDocument(); }
-    Element* rootEditableElement() const
-    {
-        Node* container = computeContainerNode();
-        return container ? container->rootEditableElement() : 0;
-    }
 
     bool isNull() const { return !m_anchorNode; }
     bool isNotNull() const { return m_anchorNode; }
     bool isOrphan() const { return m_anchorNode && !m_anchorNode->inDocument(); }
 
     // Move up or down the DOM by one position.
     // Offsets are computed using layout text for nodes that have layoutObjects - but note that even when
     // using composed characters, the result may be inside a single user-visible character if a ligature is formed.
     PositionAlgorithm<Strategy> previous(PositionMoveType = CodePoint) const;
     PositionAlgorithm<Strategy> next(PositionMoveType = CodePoint) const;
@@ skipping 269 matching lines @@
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showTree(const blink::Position&);
 void showTree(const blink::Position*);
 #endif
 
 #endif // Position_h