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

Source/core/editing/commands/InsertTextCommand.cpp

 /*
  * Copyright (C) 2005 Apple Computer, 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 @@
         startPosition = positionBeforeStartNode;
     if (!isVisuallyEquivalentCandidate(startPosition))
         startPosition = startPosition.downstream();
 
     startPosition = positionAvoidingSpecialElementBoundary(startPosition);
 
     Position endPosition;
 
     if (m_text == "\t") {
         endPosition = insertTab(startPosition);
-        startPosition = endPosition.previous();
+        // TODO(yosin) We should use |PositionMoveType::Character| for
+        // |previousPositionOf()|.
+        startPosition = previousPositionOf(endPosition, PositionMoveType::Character);
         if (placeholder.isNotNull())
             removePlaceholderAt(placeholder);
     } else {
         // Make sure the document is set up to receive m_text
         startPosition = positionInsideTextNode(startPosition);
         ASSERT(startPosition.isOffsetInAnchor());
         ASSERT(startPosition.computeContainerNode());
         ASSERT(startPosition.computeContainerNode()->isTextNode());
         if (placeholder.isNotNull())
             removePlaceholderAt(placeholder);
@@ skipping 64 matching lines @@
                 splitTextNode(textNode, offset);
             insertNodeBefore(spanElement, textNode.release());
         }
     }
 
     // return the position following the new tab
     return lastPositionInNode(spanElement.get());
 }
 
 }