Move {next,previous}PositionOf() for VisiblePosition to VisibleUnits.cpp

Source/core/editing/PlainTextRange.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2005 Alexey Proskuryakov.
  *
  * 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
@@ skipping 14 matching lines @@
  */
 
 #include "config.h"
 #include "core/editing/PlainTextRange.h"
 
 #include "core/dom/ContainerNode.h"
 #include "core/dom/Document.h"
 #include "core/dom/Range.h"
 #include "core/editing/EphemeralRange.h"
 #include "core/editing/VisiblePosition.h"
+#include "core/editing/VisibleUnits.h"
 #include "core/editing/iterators/TextIterator.h"
 
 namespace blink {
 
 PlainTextRange::PlainTextRange()
     : m_start(kNotFound)
     , m_end(kNotFound)
 {
 }
 
@@ skipping 135 matching lines @@
 
     return PlainTextRange(start, end);
 }
 
 PlainTextRange PlainTextRange::create(const ContainerNode& scope, const Range& range)
 {
     return create(scope, EphemeralRange(&range));
 }
 
 }