Have different text for apps and regular extensions in some more places.

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 685 matching lines @@
         <message name="IDS_UPGRADE_AVAILABLE_BUTTON" desc="Diplayed on a button the user can use to upgrade the a more recent version of the application. [Length: 10em]">
           Update
         </message>
       </if>
 
       <!-- Extension/App install prompt -->
       <message name="IDS_EXTENSION_INLINE_INSTALL_PROMPT_TITLE" desc="Titlebar of the extension or app inline installation prompt window">
         Add to Chromium
       </message>
 
-      <!-- Extension alerts. -->
-      <message name="IDS_EXTENSION_ALERT_ITEM_EXTERNAL" desc="A statement that an external extension has been newly installed. End users have no idea what an 'external' extension is, so we simply call them extensions. The trailing character must be a newline.">
-The extension "<ph name="EXTENSION_NAME">$1<ex>Gmail Checker</ex></ph>" has been added.
-
-'''
-      </message>
-
       <!-- Extension installed bubble -->
       <message name="IDS_EXTENSION_INSTALLED_HEADING" desc="First line in the content area of the extension installed bubble. Instructs that the extension was installed.">
         <ph name="EXTENSION_NAME">$1<ex>Gmail Checker</ex></ph> has been added to Chromium.
       </message>
 
       <!-- chrome://settings/extensions page -->
       <message name="IDS_EXTENSIONS_INCOGNITO_WARNING" desc="Warns the user that Chromium cannot prevent extensions from recording history in incognito mode. Displayed in extensions management UI after an extension is selected to be run in incognito mode.">
         <ph name="BEGIN_BOLD">&lt;b&gt;</ph>Warning:<ph name="END_BOLD">&lt;/b&gt;</ph> Chromium cannot prevent extensions from recording your browsing history. To disable this extension in incognito mode, unselect this option.
       </message>
       <message name="IDS_EXTENSIONS_UNINSTALL" desc="The link for uninstalling extensions.">
@@ skipping 169 matching lines @@
 
       <!-- Chrome OS keyboard overlay-->
       <if expr="pp_ifdef('chromeos')">
         <message name="IDS_KEYBOARD_OVERLAY_SHOW_WRENCH_MENU" desc="The text in the keyboard overlay to explain the shortcut that opens the main Chrome menu.">
           Show the Chromium menu
         </message>
       </if>
     </messages>
   </release>
 </grit>