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

Source/core/layout/LayoutView.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 785 matching lines @@
     if (!selection.isRange()) {
         clearSelection();
         return;
     }
 
     // Use the rightmost candidate for the start of the selection, and the leftmost candidate for the end of the selection.
     // Example: foo <a>bar</a>.  Imagine that a line wrap occurs after 'foo', and that 'bar' is selected.   If we pass [foo, 3]
     // as the start of the selection, the selection painting code will think that content on the line containing 'foo' is selected
     // and will fill the gap before 'bar'.
     PositionType startPos = Strategy::selectionStart(selection);
-    PositionType candidate = mostBackwardCaretPosition(startPos);
+    PositionType candidate = startPos.downstream();
     if (isVisuallyEquivalentCandidate(candidate))
         startPos = candidate;
     PositionType endPos = Strategy::selectionEnd(selection);
-    candidate = mostForwardCaretPosition(endPos);
+    candidate = endPos.upstream();
     if (isVisuallyEquivalentCandidate(candidate))
         endPos = candidate;
 
     // We can get into a state where the selection endpoints map to the same VisiblePosition when a selection is deleted
     // because we don't yet notify the FrameSelection of text removal.
     if (startPos.isNull() || endPos.isNull() || Strategy::selectionVisibleStart(selection).deepEquivalent() == Strategy::selectionVisibleEnd(selection).deepEquivalent())
         return;
     LayoutObject* startLayoutObject = startPos.anchorNode()->layoutObject();
     LayoutObject* endLayoutObject = endPos.anchorNode()->layoutObject();
     if (!startLayoutObject || !endLayoutObject)
@@ skipping 185 matching lines @@
     return viewHeight(IncludeScrollbars) / scale;
 }
 
 void LayoutView::willBeDestroyed()
 {
     LayoutBlockFlow::willBeDestroyed();
     m_compositor.clear();
 }
 
 } // namespace blink