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

chrome/app/chromium_strings.grd

Index: chrome/app/chromium_strings.grd
diff --git a/chrome/app/chromium_strings.grd b/chrome/app/chromium_strings.grd
index d14b7147d3258b8db0a9fe4e540e1b76e0bffaa9..87493d067f5d44d49abcf032179507100079ff14 100644
--- a/chrome/app/chromium_strings.grd
+++ b/chrome/app/chromium_strings.grd
@@ -456,6 +456,9 @@ Chromium is unable to recover your settings.
         <message name="IDS_INSTALL_MULTI_INSTALLATION_EXISTS" desc="Error during install if a multi-install Chromium is present, thereby preventing the installation of a single-install Chromium.">
           A conflicting installation of Chromium 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.">
+          Chromium 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.">