Provide a message to Google Update for the user when a system-level Chrome is already installed.

chrome/app/google_chrome_strings.grd

Index: chrome/app/google_chrome_strings.grd
diff --git a/chrome/app/google_chrome_strings.grd b/chrome/app/google_chrome_strings.grd
index 7bc8a80810767d4b05e9d4e598e0648cfc574d60..a805f9e1e91cdffb5d93d46fa07aa3223e65ba7f 100644
--- a/chrome/app/google_chrome_strings.grd
+++ b/chrome/app/google_chrome_strings.grd
@@ -457,6 +457,9 @@ Google Chrome is unable to recover your settings.
         <message name="IDS_INSTALL_MULTI_INSTALLATION_EXISTS" desc="Error during install if a multi-install Google Chrome is present, thereby preventing the installation of a single-install Google Chrome.">
           A conflicting installation of Google Chrome was found on the system. Please uninstall it and try again.
         </message>
+        <message name="IDS_INSTALL_EXISTING_VERSION_LAUNCHED" desc="A message shown to users who try to install Chrome in their user profile directory when their computer already has Chrome installed for all users. In this case, the installer silently launches the existing version of Chrome for all users rather than installing a second version of Chrome.">
+          Google Chrome is already installed for all users on your computer.
+        </message>
       </if>
       <!-- Options Dialog -->
       <message name="IDS_OPTIONS_IMPROVE_BROWSING_EXPERIENCE" desc="The text in the options panel that describes how we use web services to improve browsing experience.">