Support rollback with installerdata in mini_installer

chrome/installer/setup/setup_util.h

Index: chrome/installer/setup/setup_util.h
diff --git a/chrome/installer/setup/setup_util.h b/chrome/installer/setup/setup_util.h
index c6ab66146f65e2911b7a077667abcf39e4710a2c..c48a0b7437699ecbc15b0daa1b635fd76f8582d6 100644
--- a/chrome/installer/setup/setup_util.h
+++ b/chrome/installer/setup/setup_util.h
@@ -33,6 +33,7 @@ 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
@@ -120,6 +121,9 @@ void DeleteRegistryKeyPartial(
 // registry entries.
 base::string16 GuidToSquid(const base::string16& guid);
 
+// Returns true if downgrade is allowed by installer data.
+bool IsDowngradeAllowed(const MasterPreferences& prefs);
+
 // 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