Convert remaining instances of the 'os' variable in grit conditions

ui/base/strings/app_locale_settings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 <grit latest_public_release="0" current_release="1">
   <outputs>
     <output filename="grit/app_locale_settings.h" type="rc_header">
       <emit emit_type='prepend'></emit>
     </output>
     <output filename="app_locale_settings_am.rc" type="rc_all" lang="am" />
     <output filename="app_locale_settings_ar.rc" type="rc_all" lang="ar" />
     <output filename="app_locale_settings_bg.rc" type="rc_all" lang="bg" />
     <output filename="app_locale_settings_bn.rc" type="rc_all" lang="bn" />
@@ skipping 192 matching lines @@
       <!-- The UI font used in native UI components (e.g. menu). 'default'
            indicates that the font obtained from the system be used.
            Otherwise, the system default UI font will be overriden with
            the family specified. This should be default for locales
            other than Indian locales.
            TODO(jungshik): This and IDS_UI_FONT_SIZE_SCALER are only used
            on Windows now and are likely to be so in the future because Mac and 
            Linux fonts do not have the issue Windows fonts for some locales
            (Indian) have. In that case, this need to be enclosed
            by platform-dependent if-clause. -->
-      <if expr="os == 'win32'">
+      <if expr="is_win">
         <message name="IDS_UI_FONT_FAMILY" use_name_for_id="true">
           default
         </message>
         <!-- For Windows XP -->
         <message name="IDS_UI_FONT_FAMILY_XP" use_name_for_id="true">
           default
         </message>
 
         <!-- To get the actual UI font size for native UI components
              (e.g. menu), the system UI font size is scaled with this value/100.
@@ skipping 14 matching lines @@
       <!-- For Chrome OS -->
       <if expr="pp_ifdef('chromeos')">
         <!-- The font name like: 'Font Name, 10' -->
         <message name="IDS_UI_FONT_FAMILY_CROS" use_name_for_id="true">
           default
         </message>
       </if>
     </messages>
   </release>
 </grit>