Move a member function atEditingBoundary() out from PositionAlgorithm<Strategy> template class

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 169 matching lines @@
     static int uncheckedNextOffset(const Node*, int current);
 
     int compareTo(const PositionAlgorithm<Strategy>&) const;
 
     // These can be either inside or just before/after the node, depending on
     // if the node is ignored by editing or not.
     // FIXME: These should go away. They only make sense for legacy positions.
     bool atFirstEditingPositionForNode() const;
     bool atLastEditingPositionForNode() const;
 
-    // Returns true if the visually equivalent positions around have different editability
-    bool atEditingBoundary() const;
     Node* parentEditingBoundary() const;
 
     bool atStartOfTree() const;
     bool atEndOfTree() const;
 
     // These return useful visually equivalent positions.
     PositionAlgorithm<Strategy> upstream(EditingBoundaryCrossingRule = CannotCrossEditingBoundary) const;
     PositionAlgorithm<Strategy> downstream(EditingBoundaryCrossingRule = CannotCrossEditingBoundary) const;
 
     bool isCandidate() const;
@@ skipping 245 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