Expose HTML pre tag with correct MSAA+IA2 Role

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 126 matching lines @@
     menu_list_option,
     menu_list_popup,
     menu,
     meter,
     navigation,
     note,
     outline,
     pane,
     paragraph,
     pop_up_button,
+    pre,
     presentational,
     progress_indicator,
     radio_button,
     radio_group,
     region,
     root_web_area,
     row_header,
     row,
     ruler_marker,
     ruler,
@@ skipping 221 matching lines @@
     word_ends
   };
 
   [cpp_enum_prefix_override="ax"] enum AXTextDirection {
     text_direction_lr,
     text_direction_rl,
     text_direction_tb,
     text_direction_bt
   };
 };