Get rid of redundant member function PositionAlgorithm<Strategy>::{upstream,downstream}

Source/core/editing/EditingStyle.cpp

 /*
  * Copyright (C) 2007, 2008, 2009 Apple Computer, Inc.
  * Copyright (C) 2010, 2011 Google 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 1335 matching lines @@
     return style;
 }
 
 WritingDirection EditingStyle::textDirectionForSelection(const VisibleSelection& selection, EditingStyle* typingStyle, bool& hasNestedOrMultipleEmbeddings)
 {
     hasNestedOrMultipleEmbeddings = true;
 
     if (selection.isNone())
         return NaturalWritingDirection;
 
-    Position position = selection.start().downstream();
+    Position position = mostForwardCaretPosition(selection.start());
 
     Node* node = position.anchorNode();
     if (!node)
         return NaturalWritingDirection;
 
     Position end;
     if (selection.isRange()) {
-        end = selection.end().upstream();
+        end = mostBackwardCaretPosition(selection.end());
 
         ASSERT(end.document());
         Node* pastLast = Range::create(*end.document(), position.parentAnchoredEquivalent(), end.parentAnchoredEquivalent())->pastLastNode();
         for (Node* n = node; n && n != pastLast; n = NodeTraversal::next(*n)) {
             if (!n->isStyledElement())
                 continue;
 
             RefPtrWillBeRawPtr<CSSComputedStyleDeclaration> style = CSSComputedStyleDeclaration::create(n);
             RefPtrWillBeRawPtr<CSSValue> unicodeBidi = style->getPropertyCSSValue(CSSPropertyUnicodeBidi);
             if (!unicodeBidi || !unicodeBidi->isPrimitiveValue())
@@ skipping 343 matching lines @@
 {
     for (Node* ancestor = node; ancestor; ancestor = ancestor->parentNode()) {
         RefPtrWillBeRawPtr<CSSComputedStyleDeclaration> ancestorStyle = CSSComputedStyleDeclaration::create(ancestor);
         if (!hasTransparentBackgroundColor(ancestorStyle.get()))
             return ancestorStyle->getPropertyCSSValue(CSSPropertyBackgroundColor);
     }
     return nullptr;
 }
 
 }