Support rollback with installerdata in mini_installer

chrome/installer/setup/setup_util.h

 // 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 declares util functions for setup project. It also declares a
 // few functions that the Chrome component updater uses for patching binary
 // deltas.
 
 #ifndef CHROME_INSTALLER_SETUP_SETUP_UTIL_H_
 #define CHROME_INSTALLER_SETUP_SETUP_UTIL_H_
@@ skipping 15 matching lines @@
 class CommandLine;
 class FilePath;
 class Version;
 }
 
 namespace installer {
 
 class InstallationState;
 class InstallerState;
 class ProductState;
+class MasterPreferences;
 
 // Applies a patch file to source file using Courgette. Returns 0 in case of
 // success. In case of errors, it returns kCourgetteErrorOffset + a Courgette
 // status code, as defined in courgette/courgette.h
 int CourgettePatchFiles(const base::FilePath& src,
                         const base::FilePath& patch,
                         const base::FilePath& dest);
 
 // Applies a patch file to source file using bsdiff. This function uses
 // Courgette's flavor of bsdiff. Returns 0 in case of success, or
@@ skipping 67 matching lines @@
 // The key itself is deleted if no subkeys are preserved.
 void DeleteRegistryKeyPartial(
     HKEY root,
     const base::string16& path,
     const std::vector<base::string16>& keys_to_preserve);
 
 // Converts a product GUID into a SQuished gUID that is used for MSI installer
 // registry entries.
 base::string16 GuidToSquid(const base::string16& guid);
 
+// Returns true if downgrade is allowed by installer data.
+bool CanDowngradeVersion(const MasterPreferences& prefs);

[grt (UTC plus 2), 2016/04/28 16:55:30]

IsDowngradeAllowed?

[zmin, 2016/04/28 17:51:29]

Actually I love this one. How about you, @georgesak?

+
 // This class will enable the privilege defined by |privilege_name| on the
 // current process' token. The privilege will be disabled upon the
 // ScopedTokenPrivilege's destruction (unless it was already enabled when the
 // ScopedTokenPrivilege object was constructed).
 // Some privileges might require admin rights to be enabled (check is_enabled()
 // to know whether |privilege_name| was successfully enabled).
 class ScopedTokenPrivilege {
  public:
   explicit ScopedTokenPrivilege(const wchar_t* privilege_name);
   ~ScopedTokenPrivilege();
@@ skipping 12 matching lines @@
   // The previous state of the privilege this object is responsible for. As set
   // by AdjustTokenPrivileges() upon construction.
   TOKEN_PRIVILEGES previous_privileges_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(ScopedTokenPrivilege);
 };
 
 }  // namespace installer
 
 #endif  // CHROME_INSTALLER_SETUP_SETUP_UTIL_H_