Introduce composed tree version of canonicalPosition() in VisiblePosition

Source/core/editing/VisiblePosition.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Portions Copyright (c) 2011 Motorola Mobility, 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
@@ skipping 619 matching lines @@
         return prev;
 
     return next;
 }
 
 Position canonicalPositionOf(const Position& position)
 {
     return canonicalPosition(position);
 }
 
+PositionInComposedTree canonicalPositionOf(const PositionInComposedTree& position)
+{
+    return canonicalPosition(position);
+}
+
 template<typename PositionType>
 void VisiblePosition::init(const PositionType& position, EAffinity affinity)
 {
     m_affinity = affinity;
 
     m_deepPosition = canonicalPosition(position);
 
     if (m_affinity != UPSTREAM)
         return;
 
@@ skipping 175 matching lines @@
     else
         fprintf(stderr, "Cannot showTree for (nil) VisiblePosition.\n");
 }
 
 void showTree(const blink::VisiblePosition& vpos)
 {
     vpos.showTreeForThis();
 }
 
 #endif