Move {left,right}PositionOf() for VisiblePosition to VisibleUnits.cpp

Source/core/editing/VisiblePosition.h

 /*
  * Copyright (C) 2004, 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 94 matching lines @@
     void showTreeForThis() const;
 #endif
 
 private:
     // TODO(yosin) We should use |PositionWithAffinity| to make
     // |toPositionWithAffinity()| simpler.
     Position m_deepPosition;
     TextAffinity m_affinity;
 };
 
-// TODO(yosin) We should move |leftPositionOf()| and |rightPositionOf()| to
-// "VisibleUnits.cpp".
-VisiblePosition leftPositionOf(const VisiblePosition&);
-VisiblePosition rightPositionOf(const VisiblePosition&);
-
 // TODO(yosin) We should move |honorEditingBoundaryAtOr{Before,After} to
 // "VisibleUnits.cpp" as static function.
 // next() and previous() will increment/decrement by a character cluster.
 VisiblePosition honorEditingBoundaryAtOrBefore(const VisiblePosition&, const Position& anchor);
 PositionWithAffinity honorEditingBoundaryAtOrBeforeOf(const PositionWithAffinity&, const Position& anchor);
 PositionInComposedTreeWithAffinity honorEditingBoundaryAtOrBeforeOf(const PositionInComposedTreeWithAffinity&, const PositionInComposedTree& anchor);
 VisiblePosition honorEditingBoundaryAtOrAfter(const VisiblePosition&, const Position& anchor);
 
 CORE_EXPORT VisiblePosition createVisiblePosition(const Position&, TextAffinity = VP_DEFAULT_AFFINITY);
 CORE_EXPORT VisiblePosition createVisiblePosition(const PositionWithAffinity&);
 CORE_EXPORT VisiblePosition createVisiblePosition(const PositionInComposedTree&, TextAffinity = VP_DEFAULT_AFFINITY);
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showTree(const blink::VisiblePosition*);
 void showTree(const blink::VisiblePosition&);
 #endif
 
 #endif // VisiblePosition_h