Add AX role ,'AXDescriptionList', for dl element(re-land).

Source/core/accessibility/AXList.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 38 matching lines @@
 PassRefPtr<AXList> AXList::create(RenderObject* renderer)
 {
     return adoptRef(new AXList(renderer));
 }
 
 bool AXList::computeAccessibilityIsIgnored() const
 {
     return accessibilityIsIgnoredByDefault();
 }
 
+bool AXList::isDescriptionList() const
+{
+    if (!m_renderer)
+        return false;
+
+    Node* node = m_renderer->node();
+    return node && node->hasTagName(dlTag);
+}
+
+AccessibilityRole AXList::roleValue() const
+{
+    if (isDescriptionList())
+        return DescriptionListRole;
+
+    return ListRole;
+}
 } // namespace blink