Added Aura notification that relaunch and powerwash is required in case of downgrade.

ash/system/tray/system_tray_delegate.cc

Index: ash/system/tray/system_tray_delegate.cc
diff --git a/ash/system/tray/system_tray_delegate.cc b/ash/system/tray/system_tray_delegate.cc
index d0b9fb17b7a58f9d5c72de80ad960b2e5e12409b..c1cf4b4d0d7155cf622fd68e9d77deb979ca8ac5 100644
--- a/ash/system/tray/system_tray_delegate.cc
+++ b/ash/system/tray/system_tray_delegate.cc
@@ -40,4 +40,13 @@ IMEPropertyInfo::IMEPropertyInfo()
 IMEPropertyInfo::~IMEPropertyInfo() {
 }
 
+UpdateInfo::UpdateInfo()
+    : severity(UPDATE_NORMAL),
+      update_required(false),
+      factory_reset_required(false) {
+}
+
+UpdateInfo::~UpdateInfo() {
+}
+
 }  // namespace ash