Introduce background.scripts feature for extension manifests.

chrome/app/generated_resources.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!--
 This file contains definitions of resources that will be translated for each
 locale.  The variables is_win, is_macosx, is_linux, and is_posix are available
 for making strings OS specific.  Other platform defines such as use_titlecase
 are declared in build/common.gypi.
 -->
 
 <grit base_dir="." latest_public_release="0" current_release="1"
@@ skipping 4154 matching lines @@
       </message>
       <message name="IDS_EXTENSION_LOAD_PLUGIN_PATH_FAILED" desc="">
         Could not load '<ph name="PLUGIN_PATH">$1<ex>/path/to/file</ex></ph>' for plugin.
       </message>
       <message name="IDS_EXTENSION_LOAD_ICON_FOR_PAGE_ACTION_FAILED" desc="">
         Could not load icon '<ph name="ICON">$1<ex>icon.png</ex></ph>' for page action.
       </message>
       <message name="IDS_EXTENSION_LOAD_ICON_FOR_BROWSER_ACTION_FAILED" desc="">
         Could not load icon '<ph name="ICON">$1<ex>icon.png</ex></ph>' for browser action.
       </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_OPTIONS_PAGE_FAILED" desc="">
         Could not load options page '<ph name="OPTIONS_PAGE">$1<ex>page.html</ex></ph>'.
       </message>
       <if expr="is_win">
         <message name="IDS_EXTENSION_UNPACK_FAILED" desc="On windows, it is possible to mount a disk without the root of that disk having a drive letter.  The sandbox does not support this. See crbug/49530 .">
           Can not unpack extension.  To safely unpack an extension, there must be a path to your profile directory that starts with a drive letter and does not contain a junction, mount point, or symlink.  No such path exists for your profile.
         </message>
@@ skipping 10618 matching lines @@
     </messages>
     <structures fallback_to_english="true">
       <!-- Make sure these stay in sync with the structures in generated_resources.grd. -->
       <structure name="IDD_CHROME_FRAME_FIND_DIALOG" file="cf_resources.rc" type="dialog" >
       </structure>
       <structure name="IDD_CHROME_FRAME_READY_PROMPT" file="cf_resources.rc" type="dialog" >
       </structure>
     </structures>
   </release>
 </grit>