Hook up guest browser plugins to 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.
 
 // 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 301 matching lines @@
     aria_readonly,
 
     // Writeable attributes
     can_set_value,
 
     // If this is set, all of the other fields in this struct should
     // be ignored and only the locations should change.
     update_location_only,
 
     // Set on a canvas element if it has fallback content.
-    canvas_has_fallback
+    canvas_has_fallback,
+
+    // Set if this node is the host of an external AXTree, for
+    // example a web view that's a child of a native view, or a
+    // web iframe that's the child of another web frame.
+    is_ax_tree_host
   };
 
   [cpp_enum_prefix_override="ax_attr"] enum AXIntListAttribute {
     // Ids of nodes that are children of this node logically, but are
     // not children of this node in the tree structure. As an example,
     // a table cell is a child of a row, and an 'indirect' child of a
     // column.
     indirect_child_ids,
 
     // Relationships between this element and other elements.
@@ skipping 29 matching lines @@
     word_ends
   };
 
   [cpp_enum_prefix_override="ax"] enum AXTextDirection {
     text_direction_lr,
     text_direction_rl,
     text_direction_tb,
     text_direction_bt
   };
 };