Add recommended extension installation support

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 245 matching lines @@
         Access photos, music, and other media from your computer
       </message>
 
       <!-- Policy strings. Please keep alphabetized. -->
       <message name="IDS_EXTENSION_CANT_INSTALL_POLICY_BLOCKED" desc="Error message when a user tries to install an extension that is blocked by administrator policy.">
         <ph name="EXTENSION_NAME">$1<ex>Google Talk</ex></ph> (extension ID "<ph name="EXTENSION_ID">$2<ex>nckgahadagoaajjgafhacjanaoiihapd</ex></ph>") is blocked by the administrator.
       </message>
       <message name="IDS_EXTENSION_CANT_MODIFY_POLICY_REQUIRED" desc="Error message when a user tries to remove or change an extension that is required by administrator policy.">
         The administrator of this machine requires <ph name="EXTENSION_NAME">$1<ex>Google Talk</ex></ph> to be installed. It cannot be removed or modified.
       </message>
+      <message name="IDS_EXTENSION_CANT_UNINSTALL_POLICY_REQUIRED" desc="Error message when a user tries to uninstall an extension that is required by administrator policy.">
+        The administrator of this machine requires <ph name="EXTENSION_NAME">$1<ex>Google Talk</ex></ph> to be installed. It cannot be uninstalled.
+      </message>
 
       <!-- Settings override strings. Please keep alphabetized. -->
       <message name="IDS_EXTENSION_PROMPT_WARNING_HOME_PAGE_SETTING_OVERRIDE" desc="Permission string for home page override.">
         Change your home page to: <ph name="HOME_PAGE">$1<ex>home.page.com/home.html</ex></ph>
       </message>
       <message name="IDS_EXTENSION_PROMPT_WARNING_SEARCH_SETTINGS_OVERRIDE" desc="Permission string for search settings override.">
         Change your search settings to: <ph name="SEARCH_HOST">$1<ex>url.search.com</ex></ph>
       </message>
       <message name="IDS_EXTENSION_PROMPT_WARNING_START_PAGE_SETTING_OVERRIDE" desc="Permission string for start page override.">
         Change your start page to: <ph name="START_PAGE">$1<ex>start.page.com/start.html</ex></ph>
@@ skipping 88 matching lines @@
       <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>