Add support for retrieving image thumbnails as part of the accessibility tree.

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.
 
 // TODO(nektar): Migrate entire file to Mojoq.
 // 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 four enums, also add to
@@ skipping 20 matching lines @@
     autocorrection_occured,    // Unknown: http://crbug.com/392498
     blur,                      // Remove: http://crbug.com/392502
     checked_state_changed,     // Implicit
     children_changed,
     clicked,
     document_selection_changed,
     expanded_changed,          // Web
     focus,
     hide,                      // Remove: http://crbug.com/392502
     hover,
+    image_frame_updated,       // Web
     invalid_status_changed,    // Implicit
     layout_complete,           // Web
     live_region_created,       // Implicit
     live_region_changed,       // Web
     load_complete,             // Web
     location_changed,          // Web
     menu_end,                  // Native / Win
     menu_list_item_selected,   // Web
     menu_list_value_changed,   // Web
     menu_popup_end,            // Native / Win
@@ skipping 184 matching lines @@
     blur,
 
     // Decrement a slider or range control by one step value.
     decrement,
 
     // Do the default action for an object, typically this means "click".
     do_default,
 
     focus,
 
+    // Return the content of this image object in the image_data attribute.
+    get_image_data,
+
     // Given a point, find the object it corresponds to and fire a
     // HOVER event on it in response.
     hit_test,
 
     // Increment a slider or range control by one step value.
     increment,
 
     // Delete any selected text in the control's text value and
     // insert |AXActionData::value| in its place, like when typing or pasting.
     replace_selected_text,
@@ skipping 42 matching lines @@
     // Only used when invalid_state == invalid_state_other.
     aria_invalid_value,
     auto_complete,
     container_live_relevant,
     container_live_status,
     description,
     display,
     // Only present when different from parent.
     font_family,
     html_tag,
+    image_data_url,
     // Only present when different from parent.
     language,
     name,
     live_relevant,
     live_status,
     placeholder,
     role,
     shortcut,
     url,
     value
@@ skipping 286 matching lines @@
     // First node is before the second one.
     before,
 
     // Nodes are the same.
     equal,
 
     // First node is after the second one.
     after
   };
 };