Revert of [Editing][Codehealth] Replace Position::uptream/downstream to mostBackward/ForwardCaretPosition.

Source/core/layout/LayoutObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 2974 matching lines @@
     return node && node->isElementNode() ? toElement(node) : nullptr;
 }
 
 PositionWithAffinity LayoutObject::createPositionWithAffinity(int offset, TextAffinity affinity)
 {
     // If this is a non-anonymous layoutObject in an editable area, then it's simple.
     if (Node* node = nonPseudoNode()) {
         if (!node->hasEditableStyle()) {
             // If it can be found, we prefer a visually equivalent position that is editable.
             const Position position = Position(node, offset);
-            Position candidate = mostBackwardCaretPosition(position, CanCrossEditingBoundary);
+            Position candidate = position.downstream(CanCrossEditingBoundary);
             if (candidate.anchorNode()->hasEditableStyle())
                 return PositionWithAffinity(candidate, affinity);
-            candidate = mostForwardCaretPosition(position, CanCrossEditingBoundary);
+            candidate = position.upstream(CanCrossEditingBoundary);
             if (candidate.anchorNode()->hasEditableStyle())
                 return PositionWithAffinity(candidate, affinity);
         }
         // FIXME: Eliminate legacy editing positions
         return PositionWithAffinity(Position::editingPositionOf(node, offset), affinity);
     }
 
     // We don't want to cross the boundary between editable and non-editable
     // regions of the document, but that is either impossible or at least
     // extremely unlikely in any normal case because we stop as soon as we
@@ skipping 394 matching lines @@
         const blink::LayoutObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
     } else {
         fprintf(stderr, "Cannot showLayoutTree. Root is (nil)\n");
     }
 }
 
 #endif