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

chrome/app/chromium_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 <!-- This file contains definitions of strings that are distribution specific.
 These strings will not be translated and only english versions will
 be available for now. -->
 
 <grit base_dir="." latest_public_release="0" current_release="1"
       source_lang_id="en" enc_check="möl">
   <outputs>
     <output filename="grit/chromium_strings.h" type="rc_header">
       <emit emit_type='prepend'></emit>
@@ skipping 188 matching lines @@
         Chromium
       </message>
       <message name="IDS_PRODUCT_DESCRIPTION" desc="Browser description">
         Chromium is a web browser that runs web pages and applications with lightning speed. It's fast, stable, and easy to use. Browse the web more safely with malware and phishing protection built into Chromium.
       </message>
       <if expr="pp_ifdef('chromeos')">
         <message name="IDS_PRODUCT_OS_NAME" desc="The Chrome OS application name">
           Chromium OS
         </message>
       </if>
-      <if expr="os.find('win') != -1">
+      <if expr="is_win">
         <message name="IDS_PRODUCT_FRAME_NAME" desc="The Chrome Frame application name">
           Chromium Frame
         </message>
         <message name="IDS_VERSIONMISMATCH_HEADER">
           Chromium Frame Update.
         </message>
         <message name="IDS_VERSIONMISMATCH">
           Chromium Frame has been updated. Please relaunch your browser. Chrome version: <ph name="TODO_0001">%ls<ex>TODO</ex></ph>, Chromium Frame version: <ph name="TODO_0002">%ls<ex>TODO</ex></ph>
         </message>
         <message name="IDS_VERSIONUNKNOWN">
@@ skipping 323 matching lines @@
         You are viewing a secure Chromium page.
       </message>
       <!-- Print Preview -->
       <message name="IDS_PRINT_PREVIEW_NO_PLUGIN" desc="Message to display when the PDF viewer is missing.">
         Chromium does not include the PDF viewer which is required for Print Preview to function.
       </message>
       <message name="IDS_PRINT_PREVIEW_NATIVE_DIALOG" desc="Option offering the user to open the native print dialog, displayed when the PDF viewer is missing.">
         Launch native print dialog
       </message>
 
-      <if expr="os == 'darwin'">
+      <if expr="is_macosx">
         <message name="IDS_APP_MENU_PRODUCT_NAME" desc="The application's short name, used for the Mac's application menu, activity monitor, etc. This should be less than 16 characters. Example: Chrome, not Google Chrome.">
           Chromium
         </message>
         <message name="IDS_HELPER_NAME" desc="The helper application's name.  Should contain the Chrome application name (IDS_PRODUCT_NAME). Example: Google Chrome Helper.">
           Chromium Helper
         </message>
         <message name="IDS_SHORT_HELPER_NAME" desc="The helper application's short name, used for the Mac's application menu, activity monitor, etc. Example: Chrome Helper, not Google Chrome Helper.">
           Chromium Helper
         </message>
 
@@ skipping 19 matching lines @@
         <message name="IDS_UTILITY_APP_NAME" desc="The utility application's name.  Should contain the Chrome application name (IDS_PRODUCT_NAME). Example: Google Chrome Utility.">
           Chromium Utility
         </message>
         <message name="IDS_SHORT_UTILITY_APP_NAME" desc="The utility application's short name, used for the Mac's application menu, activity monitor, etc. Example: Chrome Utility, not Google Chrome Utility.">
           Chromium Utility
         </message>
       </if>
     </messages>
   </release>
 </grit>