Introduce {next,previous}PositionOf() as replacement of {next,previous}() member functions in Positi

Source/core/editing/EditingUtilities.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007 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 1137 matching lines @@
     if (position.isNull())
         return Position();
 
     Element* fromRootEditableElement = position.anchorNode()->rootEditableElement();
 
     bool atStartOfLine = isStartOfLine(VisiblePosition(position, affinity));
     bool rendered = isVisuallyEquivalentCandidate(position);
 
     Position currentPos = position;
     while (!currentPos.atStartOfTree()) {
-        currentPos = currentPos.previous();
+        // TODO(yosin) When we use |previousCharacterPosition()| other than
+        // finding leading whitespace, we should use |Character| instead of
+        // |CodePoint|.
+        currentPos = previousPositionOf(currentPos, PositionMoveType::CodePoint);
 
         if (currentPos.anchorNode()->rootEditableElement() != fromRootEditableElement)
             return position;
 
         if (atStartOfLine || !rendered) {
             if (isVisuallyEquivalentCandidate(currentPos))
                 return currentPos;
         } else if (rendersInDifferentPosition(position, currentPos)) {
             return currentPos;
         }
@@ skipping 276 matching lines @@
     // if the selection starts just before a paragraph break, skip over it
     if (isEndOfParagraph(visiblePosition))
         return visiblePosition.next().deepEquivalent().downstream();
 
     // otherwise, make sure to be at the start of the first selected node,
     // instead of possibly at the end of the last node before the selection
     return visiblePosition.deepEquivalent().downstream();
 }
 
 } // namespace blink