Make spin button accessible on Mac.

webkit/glue/webkit_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 webkit 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 276 matching lines @@
       </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_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>
 
       <message name="IDS_AX_BUTTON_ACTION_VERB" desc="Verb stating the action that will occur when a button is pressed, as used by accessibility.">
         press
       </message>
       <message name="IDS_AX_RADIO_BUTTON_ACTION_VERB" desc="Verb stating the action that will occur when a radio button is clicked, as used by accessibility.">
         select
       </message>
       <message name="IDS_AX_TEXT_FIELD_ACTION_VERB" desc="Verb stating the action that will occur when a text field is selected, as used by accessibility.">
         activate
       </message>
@@ skipping 161 matching lines @@
         Loading
       </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>