Add support for --critical-update-version to installer.

chrome/installer/util/util_constants.cc

Index: chrome/installer/util/util_constants.cc
diff --git a/chrome/installer/util/util_constants.cc b/chrome/installer/util/util_constants.cc
index c470faf31cb4e0a2038f1ec1f203ae37096d2ec0..72943a8a6233b7db70ce6eac90aa2c0e6490ebf4 100644
--- a/chrome/installer/util/util_constants.cc
+++ b/chrome/installer/util/util_constants.cc
@@ -42,6 +42,10 @@ const char kChromeSxS[] = "chrome-sxs";
 // Create Desktop and QuickLaunch shortcuts
 const char kCreateAllShortcuts[] = "create-all-shortcuts";
 
+// The version number of an update containing critical fixes, for which an
+// in-use Chrome should be restarted ASAP.
+const char kCriticalUpdateVersion[] = "critical-update-version";
+
 // Delete user profile data. This param is useful only when specified with
 // kUninstall, otherwise it is silently ignored.
 const char kDeleteProfile[] = "delete-profile";