Adds AX role for abbr tag.

ui/accessibility/ax_enums.idl

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // These should be kept in sync with third_party/WebKit/public/web/WebAXEnums.h
 // until the Chromium and Blink trees are merged.
 [camel_case_enum_to_string=true] namespace ui {
 
   // For new entries to the following three enums, also add to
   // chrome/common/extensions/api/automation.idl.
@@ skipping 46 matching lines @@
     show,                      // Remove: http://crbug.com/392502
     text_changed,
     text_selection_changed,
     tree_changed,              // Accessibility tree changed. Don't
                                // explicitly fire an accessibility event,
                                // only implicitly due to the change.
     value_changed
   };
 
   enum AXRole {
+    abbr,
     alert_dialog,
     alert,
     annotation,
     application,
     article,
     banner,
     blockquote,
     // TODO(nektar): Remove busy_indicator because it's used nowhere.
     busy_indicator,
     button,
@@ skipping 366 matching lines @@
   };
 
   [cpp_enum_prefix_override="ax"] enum AXDescriptionFrom {
     description_from_uninitialized = 0,
     description_from_attribute,
     description_from_contents,
     description_from_placeholder,
     description_from_related_element
   };
 };