[Editing][CodeHealth] Move Position::up/downstream implementation to VisibleUnit.cpp

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 168 matching lines @@
     // 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;
 
     bool atStartOfTree() const;
     bool atEndOfTree() const;
 
     // These return useful visually equivalent positions.
+    // FIXME: We should use mostForwardCaretPosition and mostBackwardPosition.
     PositionAlgorithm<Strategy> upstream(EditingBoundaryCrossingRule = CannotCrossEditingBoundary) const;
     PositionAlgorithm<Strategy> downstream(EditingBoundaryCrossingRule = CannotCrossEditingBoundary) const;
 
     bool isCandidate() const;
     bool inRenderedText() const;
 
     InlineBoxPosition computeInlineBoxPosition(TextAffinity) const;
     InlineBoxPosition computeInlineBoxPosition(TextAffinity, TextDirection primaryDirection) const;
 
     static bool nodeIsUserSelectAll(const Node*);
@@ skipping 251 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