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

Source/core/editing/commands/BreakBlockquoteCommand.cpp

 /*
  * Copyright (C) 2005 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 76 matching lines @@
 
     ASSERT(!endingSelection().isNone());
 
     if (endingSelection().isNone())
         return;
 
     VisiblePosition visiblePos = endingSelection().visibleStart();
 
     // pos is a position equivalent to the caret.  We use downstream() so that pos will
     // be in the first node that we need to move (there are a few exceptions to this, see below).
-    Position pos = endingSelection().start().downstream();
+    Position pos = mostForwardCaretPosition(endingSelection().start());
 
     // Find the top-most blockquote from the start.
     HTMLQuoteElement* topBlockquote = toHTMLQuoteElement(highestEnclosingNodeOfType(pos, isMailHTMLBlockquoteElement));
     if (!topBlockquote || !topBlockquote->parentNode())
         return;
 
     RefPtrWillBeRawPtr<HTMLBRElement> breakElement = createBreakElement(document());
 
     bool isLastVisPosInNode = isLastVisiblePositionInNode(visiblePos, topBlockquote);
 
@@ skipping 110 matching lines @@
 
     // Make sure the cloned block quote renders.
     addBlockPlaceholderIfNeeded(clonedBlockquote.get());
 
     // Put the selection right before the break.
     setEndingSelection(VisibleSelection(positionBeforeNode(breakElement.get()), TextAffinity::Downstream, endingSelection().isDirectional()));
     rebalanceWhitespace();
 }
 
 } // namespace blink