Introduce previousPositionOf() for VisiblePosition

Source/core/editing/VisibleSelection.cpp

 /*
  * Copyright (C) 2004, 2005, 2006 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 411 matching lines @@
     case LineGranularity: {
         m_start = startOfLine(VisiblePosition(m_start, m_affinity)).deepEquivalent();
         break;
     }
     case LineBoundary:
         m_start = startOfLine(VisiblePosition(m_start, m_affinity)).deepEquivalent();
         break;
     case ParagraphGranularity: {
         VisiblePosition pos(m_start, m_affinity);
         if (isStartOfLine(pos) && isEndOfEditableOrNonEditableContent(pos))
-            pos = pos.previous();
+            pos = previousPositionOf(pos);
         m_start = startOfParagraph(pos).deepEquivalent();
         break;
     }
     case DocumentBoundary:
         m_start = startOfDocument(VisiblePosition(m_start, m_affinity)).deepEquivalent();
         break;
     case ParagraphBoundary:
         m_start = startOfParagraph(VisiblePosition(m_start, m_affinity)).deepEquivalent();
         break;
     case SentenceBoundary:
@@ skipping 804 matching lines @@
     sel.showTreeForThis();
 }
 
 void showTree(const blink::VisibleSelection* sel)
 {
     if (sel)
         sel->showTreeForThis();
 }
 
 #endif