Add installer::SetupSingleton.

chrome/app/chromium_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 <!-- This file contains definitions of strings that are distribution specific.
 If you update this file, be sure also to update google_chrome_strings.grd. -->
 
 <grit base_dir="." latest_public_release="0" current_release="1"
       output_all_resource_defines="false" source_lang_id="en" enc_check="möl">
   <outputs>
     <output filename="grit/chromium_strings.h" type="rc_header">
       <emit emit_type='prepend'></emit>
     </output>
@@ skipping 420 matching lines @@
         </message>
         <message name="IDS_SETUP_PATCH_FAILED" desc="Error message when setup.exe fails to patch itself.">
           Installation failed due to unspecified error. Please download Chromium again.
         </message>
         <message name="IDS_INSTALL_OS_NOT_SUPPORTED" desc="Error displayed if OS is not supported">
           Chromium requires Windows 7 or higher.
         </message>
         <message name="IDS_INSTALL_OS_ERROR" desc="Error displayed when any Windows API call fails and we do not have more specific information.">
           An operating system error occurred during installation. Please download Chromium again.
         </message>
+        <message name="IDS_INSTALL_SINGLETON_ACQUISITION_FAILED" desc="Error displayed when the installer cannot run because another installer is already running.">
+          Another operation on Chromium is in progress. Please try again later.
+        </message>
         <message name="IDS_INSTALL_TEMP_DIR_FAILED" desc="Error displayed when we fail to create temporary directory during installation.">
           The installer couldn't create a temporary directory. Please check for free disk space and permission to install software.
         </message>
         <message name="IDS_INSTALL_UNCOMPRESSION_FAILED" desc="Error when when we can not uncompress installation archive.">
           The installer failed to uncompress archive. Please download Chromium again.
         </message>
         <message name="IDS_INSTALL_INVALID_ARCHIVE" desc="Error displayed when we can not open the installation archive.">
           The installer archive is corrupted or invalid. Please download Chromium again.
         </message>
         <message name="IDS_INSTALL_INSUFFICIENT_RIGHTS" desc="Error displayed when a non admin user tries to attempt system level install/uninstall.">
@@ skipping 806 matching lines @@
         </message>
         <message name="IDS_METRO_FLOW_LOGO_STRING_ALT"
                  desc="Alt text for the faded Chrome logo image.">
           Chromium logo
         </message>
       </if>
 
     </messages>
   </release>
 </grit>