Support rollback with installerdata in mini_installer

chrome/installer/setup/setup_util.cc

Index: chrome/installer/setup/setup_util.cc
diff --git a/chrome/installer/setup/setup_util.cc b/chrome/installer/setup/setup_util.cc
index 93826c86ad0c1409b7639320db0e7341c990d2e2..2ff7b1d6a29ece0c32c43037af658f5ea7deb29a 100644
--- a/chrome/installer/setup/setup_util.cc
+++ b/chrome/installer/setup/setup_util.cc
@@ -12,6 +12,7 @@
 #include <algorithm>
 #include <iterator>
 #include <set>
+#include <string>
 
 #include "base/command_line.h"
 #include "base/cpu.h"
@@ -31,6 +32,8 @@
 #include "chrome/installer/util/google_update_constants.h"
 #include "chrome/installer/util/installation_state.h"
 #include "chrome/installer/util/installer_state.h"
+#include "chrome/installer/util/master_preferences.h"
+#include "chrome/installer/util/master_preferences_constants.h"
 #include "chrome/installer/util/util_constants.h"
 #include "courgette/courgette.h"
 #include "courgette/third_party/bsdiff.h"
@@ -540,6 +543,12 @@ base::string16 GuidToSquid(const base::string16& guid) {
   return squid;
 }
 
+bool IsDowngradeAllowed(const MasterPreferences& prefs) {
+  bool allow_downgrade = false;
+  return prefs.GetBool(master_preferences::kAllowDowngrade, &allow_downgrade) &&
+         allow_downgrade;
+}
+
 ScopedTokenPrivilege::ScopedTokenPrivilege(const wchar_t* privilege_name)
     : is_enabled_(false) {
   HANDLE temp_handle;