Stops using SYSTEM_STATE_INDETERMINATE as it makes radio buttons appear to have a mixed state.

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 190 matching lines @@
     default,
     disabled,  // ui/views only
     editable,
     enabled,   // content only
     expanded,
     focusable,
     focused,
     haspopup,
     horizontal,
     hovered,
-    indeterminate,
     invisible,
     linked,
     multiline,
     multiselectable,
     offscreen,
     pressed,
     protected,
     read_only,
     required,
     richly_editable,
@@ skipping 111 matching lines @@
     value_for_range,
     min_value_for_range,
     max_value_for_range,
 
     // Text attributes.
     // Font size is in pixels.
     font_size
   };
 
   [cpp_enum_prefix_override="ax_attr"] enum AXBoolAttribute {
-    // True if a checkbox or radio button is in the "mixed" state.
-    button_mixed,
+    // True if an ARIA toggle button, a checkbox or
+    // a menu item checkbox is in the "mixed" state.
+    STATE_mixed,
 
     // Live region attributes.
     container_live_atomic,
     container_live_busy,
     live_atomic,
     live_busy,
 
     // ARIA readonly flag.
     aria_readonly,
 
@@ skipping 88 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
   };
 };