AXRoleDescription for html figure tag would be 'figure'.

content/app/strings/content_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 content that
 need to be translated for each locale.-->
 
 <!-- Some of these strings and string descriptions were taken from
 WebKit/win/WebCoreLocalizedStrings.cpp so we include the original license
 below:
 
@@ skipping 350 matching lines @@
       </message>
       <message name="IDS_AX_ROLE_LIST_MARKER" desc="accessibility role description for list marker">
         list marker
       </message>
       <message name="IDS_AX_ROLE_IMAGE_MAP" desc="accessibility role description for image map">
         image map
       </message>
       <message name="IDS_AX_ROLE_HEADING" desc="accessibility role description for headings">
         heading
       </message>
+      <message name="IDS_AX_ROLE_FIGURE" desc="accessibility role description for figure">
+        figure
+      </message>
       <message name="IDS_AX_ROLE_REGION" desc="accessibility role description for region">
         region
       </message>
       <if expr="is_macosx">
         <message name="IDS_AX_ROLE_FOOTER" desc="accessibility role description for footers">
           footer
         </message>
         <message name="IDS_AX_ROLE_STEPPER" desc="accessibility role description for a stepper - a control where you can use up/down arrows to increment or decrement it. The name 'stepper' is how this user interface element is described by VoiceOver on Mac OS X; the translation should be consistent with VoiceOver.">
           stepper
         </message>
@@ skipping 346 matching lines @@
         Please lengthen this text to <ph name="MIN_CHARACTERS">$2<ex>101</ex></ph> characters or more (you are currently using <ph name="CURRENT_LENGTH">$1<ex>100</ex></ph> characters).
       </message>
 
       <message name="IDS_PLUGIN_INITIALIZATION_ERROR" desc="A message displayed when a plug-in failed to load">
         Couldn't load plug-in.
       </message>
 
     </messages>
   </release>
 </grit>