Extend AXTreeSourceViews to handle aura::Window and views::Widget.

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.
 namespace ui {
   enum AXEvent {
     activedescendantchanged,
     alert,
@@ skipping 47 matching lines @@
     client,
     color_well,
     column_header,
     column,
     combo_box,
     complementary,
     content_info,
     definition,
     description_list_detail,
     description_list_term,
+    desktop,
     dialog,
     directory,
     disclosure_triangle,
     div,
     document,
     drawer,
     editable_text,
     footer,
     form,
     grid,
@@ skipping 263 matching lines @@
     ax_attr_word_ends
   };
 
   [cpp_omit_enum_type] enum AXTextDirection {
     ax_text_direction_lr,
     ax_text_direction_rl,
     ax_text_direction_tb,
     ax_text_direction_bt
   };
 };