Android: use grit target platform instead of define.

chrome/app/resources/locale_settings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 <grit latest_public_release="0" current_release="1">
   <outputs>
     <output filename="grit/locale_settings.h" type="rc_header">
       <emit emit_type='prepend'></emit>
     </output>
     <output filename="locale_settings_am.pak" type="data_package" lang="am" />
     <output filename="locale_settings_ar.pak" type="data_package" lang="ar" />
     <if expr="pp_ifdef('use_third_party_translations')">
       <output filename="locale_settings_ast.pak" type="data_package" lang="ast" />
@@ skipping 332 matching lines @@
       <!-- The URL for the webstore. -->
       <message name="IDS_WEBSTORE_URL" translateable="false">
         https://chrome.google.com/webstore?hl=[GRITLANGCODE]
       </message>
 
       <!-- The URL for Google Chrome welcome page. This is used for the pre -->
       <!-- populated thumbnails. -->
       <message name="IDS_CHROME_WELCOME_URL" translateable="false">
         http://www.google.com/chrome/intl/[GRITLANGCODE]/welcome.html
       </message>
-      <if expr="pp_ifdef('android') or pp_ifdef('ios')">
+      <if expr="is_android or pp_ifdef('ios')">
         <message name="IDS_MOBILE_WELCOME_URL" translateable="false">
           chrome://welcome
         </message>
       </if>
 
       <!-- The URL for Google Chrome privacy policy. -->
       <if expr="pp_ifdef('ios')">
         <message name="IDS_PRIVACY_POLICY_URL" translateable="false">
           http://www.google.com/chrome/intl/[GRITLANGCODE]/privacy.html
         </message>
@@ skipping 83 matching lines @@
       </message>
 
       <if expr="pp_ifdef('chromeos')">
         <message name="IDS_FACTORY_RESET_HELP_URL" translateable="false">
           http://support.google.com/chromeos/bin/answer.py?answer=183084&amp;hl=[GRITLANGCODE]
         </message>
       </if>
     </messages>
   </release>
 </grit>