Added proper extension manifest parser for launcher_page.

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 169 matching lines @@
       </message>
       <message name="IDS_EXTENSION_LOAD_BACKGROUND_SCRIPT_FAILED" desc="">
         Could not load background script '<ph name="BACKGROUND_SCRIPT">$1<ex>script.js</ex></ph>'.
       </message>
       <message name="IDS_EXTENSION_LOAD_BACKGROUND_PAGE_FAILED" desc="">
         Could not load background page '<ph name="BACKGROUND_PAGE">$1<ex>page.html</ex></ph>'.
       </message>
       <message name="IDS_EXTENSION_LOAD_ICON_FAILED" desc="">
         Could not load extension icon '<ph name="ICON">$1<ex>icon.png</ex></ph>'.
       </message>
+      <message name="IDS_EXTENSION_LOAD_LAUNCHER_PAGE_FAILED" desc="">
+        Could not load launcher page '<ph name="PAGE">$1<ex>index.html</ex></ph>'.
+      </message>
       <message name="IDS_EXTENSION_LOCALES_NO_DEFAULT_LOCALE_SPECIFIED" desc="">
         Localization used, but default_locale wasn't specified in the manifest.
       </message>
       <message name="IDS_EXTENSION_MANIFEST_UNREADABLE" desc="">
         Manifest file is missing or unreadable.
       </message>
       <message name="IDS_EXTENSION_MANIFEST_INVALID" desc="">
         Manifest file is invalid.
       </message>
       
@@ skipping 80 matching lines @@
       <message name="IDS_EXTENSION_PROMPT_WARNING_USB_DEVICE_MISSING_PRODUCT" desc="Permission string for access to a specific USB device when a product name cannot be established for a USB device.">
         Access the USB device from <ph name="VENDOR_NAME">$1<ex>Griffin Technology</ex></ph>
       </message>
       <message name="IDS_EXTENSION_PROMPT_WARNING_USB_DEVICE_MISSING_VENDOR" desc="Permission string for access to a specific USB device when a vendor name cannot be established for a USB device.">
         Access the USB device
       </message>
 
     </messages>
   </release>
 </grit>