Move extensions manifest tests to run in extensions_unittests

extensions/extensions_strings.grd

 <?xml version="1.0" encoding="utf-8"?>
 
 <!--
   Strings for the extensions module. Used mostly for low-level error messages.
   Where possible new strings should be kept in Chrome and the extensions module
   should return an error code, message flag, etc.
 -->
 
 <grit latest_public_release="0" current_release="1"
       source_lang_id="en" enc_check="möl">
@@ skipping 331 matching lines @@
       </message>
       <message name="IDS_EXTENSION_WARNINGS_DOWNLOAD_FILENAME_CONFLICT" desc="Warning message which indicates that two or more extensions tried to determine the filename of a downloaded file in a conflicting way and the modification of this extension was ignored">
         This extension failed to name the download "<ph name="ATTEMPTED_FILENAME">$1<ex>apple.png</ex></ph>" because another extension (<ph name="EXTENSION_NAME">$2<ex>My Cool Extension</ex></ph>) determined a different filename "<ph name="ACTUAL_FILENAME">$3<ex>banana.png</ex></ph>".
       </message>
       <message name="IDS_EXTENSION_WARNING_RELOAD_TOO_FREQUENT" desc="Warning message which indates that an extension got stuck in a reload loop.">
         This extension reloaded itself too frequently.
       </message>
       <message name="IDS_EXTENSION_PROMPT_WARNING_U2F_DEVICES" desc="Warning message which indicates that an extension has access to Universal 2nd Factor devices.">
         Access your Universal 2nd Factor devices
       </message>
+      <message name="IDS_EXTENSION_PROMPT_WARNING_WEB_CONNECTABLE" desc="Permission string for allowing websites to connect to extensions.">
+        Communicate with cooperating websites
+      </message>
+
     </messages>
   </release>
 </grit>