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

chromeos/dbus/update_engine_client.h

Index: chromeos/dbus/update_engine_client.h
diff --git a/chromeos/dbus/update_engine_client.h b/chromeos/dbus/update_engine_client.h
index eddd9125cb0463a1cd334f40a5a6d49e88f491e8..5f371d5bba3648741508e537ee4f66692c966d7c 100644
--- a/chromeos/dbus/update_engine_client.h
+++ b/chromeos/dbus/update_engine_client.h
@@ -5,14 +5,14 @@
 #ifndef CHROMEOS_DBUS_UPDATE_ENGINE_CLIENT_H_
 #define CHROMEOS_DBUS_UPDATE_ENGINE_CLIENT_H_
 
+#include <string>
+
 #include "base/callback.h"
 #include "base/observer_list.h"
 #include "chromeos/chromeos_export.h"
 #include "chromeos/dbus/dbus_client.h"
 #include "chromeos/dbus/dbus_client_implementation_type.h"
 
-#include <string>
-
 namespace chromeos {
 
 // UpdateEngineClient is used to communicate with the update engine.
@@ -134,6 +134,10 @@ class CHROMEOS_EXPORT UpdateEngineClient : public DBusClient {
   // Creates the instance.
   static UpdateEngineClient* Create(DBusClientImplementationType type);
 
+  // Returns true if |target_channel| is more stable than |current_channel|.
+  static bool IsTargetChannelMoreStable(const std::string& current_channel,
+                                        const std::string& target_channel);
+
  protected:
   // Create() should be used instead.
   UpdateEngineClient();