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

Source/core/accessibility/AXObject.h

 /*
  * Copyright (C) 2008, 2009, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nuanti Ltd.
  *
  * 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.
@@ skipping 64 matching lines @@
     ColorWellRole,
     ColumnHeaderRole,
     ColumnRole,
     ComboBoxRole,
     ComplementaryRole,
     ContentInfoRole,
     DateRole,
     DateTimeRole,
     DefinitionRole,
     DescriptionListDetailRole,
+    DescriptionListRole,
     DescriptionListTermRole,
     DetailsRole,
     DialogRole,
     DirectoryRole,
     DisclosureTriangleRole,
     DivRole,
     DocumentRole,
     DrawerRole,
     EditableTextRole,
     EmbeddedObjectRole,
@@ skipping 487 matching lines @@
 
     bool m_detached;
 };
 
 #define DEFINE_AX_OBJECT_TYPE_CASTS(thisType, predicate) \
     DEFINE_TYPE_CASTS(thisType, AXObject, object, object->predicate, object.predicate)
 
 } // namespace blink
 
 #endif // AXObject_h