Get rid of a redundant argument DOWNSTREAM from VisiblePosition constructor call sites

Source/modules/accessibility/AXLayoutObject.cpp

 /*
 * Copyright (C) 2008 Apple 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 2158 matching lines @@
         return toLayoutTextControl(m_layoutObject)->textFormControlElement()->visiblePositionForIndex(index);
 
     if (!allowsTextRanges() && !m_layoutObject->isText())
         return VisiblePosition();
 
     Node* node = m_layoutObject->node();
     if (!node)
         return VisiblePosition();
 
     if (index <= 0)
-        return VisiblePosition(firstPositionInOrBeforeNode(node), DOWNSTREAM);
+        return VisiblePosition(firstPositionInOrBeforeNode(node));
 
     Position start, end;
     bool selected = Range::selectNodeContents(node, start, end);
     if (!selected)
         return VisiblePosition();
 
     CharacterIterator it(start, end);
     it.advance(index - 1);
     return VisiblePosition(Position(it.currentContainer(), it.endOffset()), UPSTREAM);
 }
@@ skipping 454 matching lines @@
         if (label && label->layoutObject()) {
             LayoutRect labelRect = axObjectCache().getOrCreate(label)->elementRect();
             result.unite(labelRect);
         }
     }
 
     return result;
 }
 
 } // namespace blink