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

chrome/installer/setup/setup_main.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/installer/setup/setup_main.h"
 
 #include <windows.h>
 #include <msi.h>
 #include <shellapi.h>
 #include <shlobj.h>
@@ skipping 527 matching lines @@
     return false;
   }
 
   const Products& products = installer_state->products();
   if (products.empty()) {
     // We haven't been given any products on which to operate.
     LOG(ERROR)
         << "Not given any products to install and no products found to update.";
     *status = installer::CHROME_NOT_INSTALLED;
     installer_state->WriteInstallerResult(*status,
-        IDS_INSTALL_NO_PRODUCTS_TO_UPDATE_BASE, NULL);
+        IDS_INSTALL_NO_PRODUCTS_TO_UPDATE_BASE, nullptr);
     return false;
   }
 
   if (!installer_state->system_install()) {
     // This is a user-level installation. Make sure that we are not installing
     // on top of an existing system-level installation.
     for (Products::const_iterator it = products.begin(); it < products.end();
          ++it) {
       const Product& product = **it;
       BrowserDistribution* browser_dist = product.distribution();
@@ skipping 24 matching lines @@
           // Instruct Google Update to launch the existing system-level Chrome.
           // There should be no error dialog.
           base::FilePath install_path(installer::GetChromeInstallPath(
               true,  // system
               browser_dist));
           if (install_path.empty()) {
             // Give up if we failed to construct the install path.
             *status = installer::OS_ERROR;
             installer_state->WriteInstallerResult(*status,
                                                   IDS_INSTALL_OS_ERROR_BASE,
-                                                  NULL);
+                                                  nullptr);
           } else {
             *status = installer::EXISTING_VERSION_LAUNCHED;
             base::FilePath chrome_exe =
                 install_path.Append(installer::kChromeExe);
             base::CommandLine cmd(chrome_exe);
             cmd.AppendSwitch(switches::kForceFirstRun);
-            installer_state->WriteInstallerResult(*status, 0, NULL);
+            installer_state->WriteInstallerResult(
+                *status, IDS_INSTALL_EXISTING_VERSION_LAUNCHED_BASE, nullptr);
             VLOG(1) << "Launching existing system-level chrome instead.";
             base::LaunchProcess(cmd, base::LaunchOptions());
           }
         } else {
           // It's no longer possible for |product| to be anything other than
           // Chrome.
           NOTREACHED();
         }
         return false;
       }
@@ skipping 1282 matching lines @@
     // never invoked directly by Google Update.
     return_code = InstallUtil::GetInstallReturnCode(install_status);
   }
 
   installer::EndPersistentHistogramStorage(installer_state.target_path(),
                                            system_install);
   VLOG(1) << "Installation complete, returning: " << return_code;
 
   return return_code;
 }