hr tag should return SplitterRole.

Source/core/accessibility/AXRenderObject.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 356 matching lines @@
         return DescriptionListTermRole;
 
     if (node && (node->hasTagName(rpTag) || node->hasTagName(rtTag)))
         return AnnotationRole;
 
     // Table sections should be ignored.
     if (m_renderer->isTableSection())
         return IgnoredRole;
 
     if (m_renderer->isHR())
-        return HorizontalRuleRole;
+        return SplitterRole;
 
     if (isHTMLOutputElement(node))
         return StatusRole;
 
     if (isHTMLParagraphElement(node))
         return ParagraphRole;
 
     if (isHTMLLabelElement(node))
         return LabelRole;
 
@@ skipping 2007 matching lines @@
         if (label && label->renderer()) {
             LayoutRect labelRect = axObjectCache()->getOrCreate(label)->elementRect();
             result.unite(labelRect);
         }
     }
 
     return result;
 }
 
 } // namespace blink