Reset user data directory and disk cache directory after downgrade.

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 <oaidl.h>
@@ skipping 210 matching lines @@
                  installer_state.system_install(),
                  dist,
                  installer_state.target_path().Append(kChromeExe),
                  is_new_install));
 }
 
 void AddProductSpecificWorkItems(const InstallationState& original_state,
                                  const InstallerState& installer_state,
                                  const base::FilePath& setup_path,
                                  const Version& new_version,
-                                 bool is_new_install,
+                                 const Version* current_version,
                                  bool add_language_identifier,
                                  WorkItemList* list) {
   const Products& products = installer_state.products();
   for (Products::const_iterator it = products.begin(); it < products.end();
        ++it) {
     const Product& p = **it;
     if (p.is_chrome()) {
       AddOsUpgradeWorkItems(installer_state, setup_path, new_version, p,
                             list);
-      AddFirewallRulesWorkItems(
-          installer_state, p.distribution(), is_new_install, list);
+      AddFirewallRulesWorkItems(installer_state, p.distribution(),
+                                current_version == nullptr, list);
 
 #if defined(GOOGLE_CHROME_BUILD)
       if (!InstallUtil::IsChromeSxSProcess()) {
         // Add items to set up the App Launcher's version key if Google Chrome
         // is being installed or updated.
         AddAppLauncherVersionKeyWorkItems(installer_state.root_key(),
             new_version, add_language_identifier, list);
       }
 #endif  // GOOGLE_CHROME_BUILD
+      InstallUtil::AddUpdateDowngradeVersionItem(installer_state.root_key(),
+                                                 *current_version, new_version,

[grt (UTC plus 2), 2016/05/20 15:25:05]

|current_version| is null on a new install, so you'll have a crash here. in this
case, i think the downgrade version should be removed from the registry; we
shouldn't treat an uninstall of N followed by an install of N-1 as a downgrade.

[zmin, 2016/05/20 16:33:05]

make sense, I'll update it.

+                                                 p.distribution(), list);
     }
     if (p.is_chrome_binaries())
       AddQuickEnableChromeFrameWorkItems(installer_state, list);
   }
 }
 
 // This is called when an MSI installation is run. It may be that a user is
 // attempting to install the MSI on top of a non-MSI managed installation. If
 // so, try and remove any existing "Add/Remove Programs" entry, as we want the
 // uninstall to be managed entirely by the MSI machinery (accessible via the
@@ skipping 850 matching lines @@
                                           KEY_WOW64_32KEY);
   }
 
 #if defined(GOOGLE_CHROME_BUILD)
   if (!InstallUtil::IsChromeSxSProcess())
     AddRemoveLegacyAppCommandsWorkItems(installer_state, install_list);
 #endif  // GOOGLE_CHROME_BUILD
 
   // Add any remaining work items that involve special settings for
   // each product.
-  AddProductSpecificWorkItems(original_state,
-                              installer_state,
-                              setup_path,
-                              new_version,
-                              current_version == NULL,
-                              add_language_identifier,
-                              install_list);
+  AddProductSpecificWorkItems(original_state, installer_state, setup_path,
+                              new_version, current_version,
+                              add_language_identifier, install_list);
 
   // Copy over brand, usagestats, and other values.
   AddGoogleUpdateWorkItems(original_state, installer_state, install_list);
 
   // Migrate usagestats back to Chrome.
   AddMigrateUsageStatesWorkItems(original_state, installer_state, install_list);
 
   // Append the tasks that run after the installation.
   AppendPostInstallTasks(installer_state,
                          setup_path,
@@ skipping 215 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