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

Source/core/editing/EditingUtilities.cpp

Index: Source/core/editing/EditingUtilities.cpp
diff --git a/Source/core/editing/EditingUtilities.cpp b/Source/core/editing/EditingUtilities.cpp
index ef8a2388c5358f944c015cbc349af4687167b704..73f9ca3fdc32d5dd501e113b5560bdb8628df84b 100644
--- a/Source/core/editing/EditingUtilities.cpp
+++ b/Source/core/editing/EditingUtilities.cpp
@@ -1155,7 +1155,10 @@ static Position previousCharacterPosition(const Position& position, TextAffinity
 
     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;