Force migrate all clients from multi-install back to single-install.

chrome/installer/setup/install_worker.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.
 //
 // This file contains the definitions of the installer functions that build
 // the WorkItemList used to install the application.
 
 #include "chrome/installer/setup/install_worker.h"
 
 #include <windows.h>  // NOLINT
@@ skipping 879 matching lines @@
 
   // Ensure that Chrome is the product being installed or updated (there are no
   // other products, so it is especially unexpected for this to fail).
   const Product* chrome_product =
       installer_state.FindProduct(BrowserDistribution::CHROME_BROWSER);
   if (!chrome_product) {
     LOG(DFATAL) << "Not operating on Chrome while migrating to single-install.";
     return;
   }
 
-  const ProductState* chrome_state = original_state.GetProductState(
-      installer_state.system_install(),
-      BrowserDistribution::CHROME_BROWSER);
-  // Bail out if there is not an existing multi-install Chrome that is being
-  // updated.
-  if (!chrome_state || !chrome_state->is_multi_install()) {
+  // Bail out if an existing multi-install Chrome is not being migrated to
+  // single-install.
+  if (!installer_state.is_migrating_to_single()) {
     VLOG(1) << "No multi-install Chrome found to migrate to single-install.";
     return;
   }
 
   const ProductState* binaries_state = original_state.GetProductState(
       installer_state.system_install(),
       BrowserDistribution::CHROME_BINARIES);
 
   // There is nothing to be done if the binaries do not have stats.
   DWORD usagestats = 0;
@@ skipping 497 matching lines @@
   // Unconditionally remove the legacy Quick Enable command from the binaries.
   // Do this even if multi-install Chrome isn't installed to ensure that it is
   // not left behind in any case.
   work_item_list->AddDeleteRegKeyWorkItem(
                       installer_state.root_key(), cmd_key, KEY_WOW64_32KEY)
       ->set_log_message("removing " + base::UTF16ToASCII(kCmdQuickEnableCf) +
                         " command");
 }
 
 }  // namespace installer