Update AX role mapping for summary to AXButton on Mac

ui/strings/ui_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!-- This file contains definitions of resources that will be translated for
 each locale. Specifically, these are UI strings that are used by app/ that
 need to be translated for each locale.-->
 
 <grit base_dir="." latest_public_release="0" current_release="1"
       output_all_resource_defines="false" source_lang_id="en" enc_check="möl">
   <outputs>
     <!-- TODO add each of your output files.  Modify the three below, and add
@@ skipping 369 matching lines @@
       </message>
       <message name="IDS_AX_UNCHECK_ACTION_VERB" desc="Verb stating the action that will occur when a checked checkbox is clicked, as used by accessibility.">
         uncheck
       </message>
 
       <!--Accessible name strings-->
       <if expr="is_macosx">
         <message name="IDS_ACCNAME_TAB_ROLE_DESCRIPTION" desc="A generic description of a tab button's role." meaning="UI element">
           Tab
         </message>
+        <message name="IDS_ACCNAME_DISCLOSURE_TRIANGLE_ROLE_DESCRIPTION" desc="A generic description of a disclosure triangle's role.">
+          Disclosure triangle
+        </message>
       </if>
       <message name="IDS_APP_ACCNAME_CLOSE" desc="The accessible name for the Close button.">
         Close
       </message>
       <message name="IDS_APP_ACCNAME_MINIMIZE" desc="The accessible name for the Minimize button.">
         Minimize
       </message>
       <message name="IDS_APP_ACCNAME_MAXIMIZE" desc="The accessible name for the Maximize button.">
         Maximize
       </message>
@@ skipping 317 matching lines @@
       <!-- Display names -->
       <message name="IDS_DISPLAY_NAME_UNKNOWN" desc="The name used for a display whose name is unknown, which is shown in the display settings and ash tray.">
         Unknown Display
       </message>
       <message name="IDS_DISPLAY_NAME_INTERNAL" desc="The name used for internal displays, which is shown in the display settings.">
         Internal Display
       </message>
     </messages>
   </release>
 </grit>