Introduce previousPositionOf() for VisiblePosition

Source/core/frame/LocalFrame.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Simon Hausmann <hausmann@kde.org>
  *                     2000 Stefan Schimanski <1Stein@gmx.de>
  *                     2001 George Staikos <staikos@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2005 Alexey Proskuryakov <ap@nypop.com>
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
@@ skipping 689 matching lines @@
     return result.innerNode() ? &result.innerNode()->document() : nullptr;
 }
 
 EphemeralRange LocalFrame::rangeForPoint(const IntPoint& framePoint)
 {
     const PositionWithAffinity positionWithAffinity = positionForPoint(framePoint);
     if (positionWithAffinity.isNull())
         return EphemeralRange();
 
     VisiblePosition position(positionWithAffinity);
-    VisiblePosition previous = position.previous();
+    VisiblePosition previous = previousPositionOf(position);
     if (previous.isNotNull()) {
         const EphemeralRange previousCharacterRange = makeRange(previous, position);
         IntRect rect = editor().firstRectForRange(previousCharacterRange);
         if (rect.contains(framePoint))
             return EphemeralRange(previousCharacterRange);
     }
 
     VisiblePosition next = position.next();
     const EphemeralRange nextCharacterRange = makeRange(position, next);
     if (nextCharacterRange.isNotNull()) {
@@ skipping 132 matching lines @@
 {
     if (isLocalRoot())
         m_instrumentingAgents = InstrumentingAgents::create();
     else
         m_instrumentingAgents = localFrameRoot()->m_instrumentingAgents;
 }
 
 DEFINE_WEAK_IDENTIFIER_MAP(LocalFrame);
 
 } // namespace blink