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

chromeos/dbus/update_engine_client.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROMEOS_DBUS_UPDATE_ENGINE_CLIENT_H_
 #define CHROMEOS_DBUS_UPDATE_ENGINE_CLIENT_H_
 
+#include <string>
+#include <vector>
+
 #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.
 class CHROMEOS_EXPORT UpdateEngineClient : public DBusClient {
  public:
   // Edges for state machine
   //    IDLE->CHECKING_FOR_UPDATE
   //    CHECKING_FOR_UPDATE->IDLE
   //    CHECKING_FOR_UPDATE->UPDATE_AVAILABLE
   //    ...
@@ skipping 101 matching lines @@
   // change). On error, calls |callback| with an empty string.
   virtual void GetChannel(bool get_current_channel,
                           const GetChannelCallback& callback) = 0;
 
   // Returns an empty UpdateCheckCallback that does nothing.
   static UpdateCheckCallback EmptyUpdateCheckCallback();
 
   // 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();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(UpdateEngineClient);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_DBUS_UPDATE_ENGINE_CLIENT_H_