cros: Add UMA metrics in migration UI to get more information from migration failures.

chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.h

 // Copyright 2017 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 CHROME_BROWSER_UI_WEBUI_CHROMEOS_LOGIN_ENCRYPTION_MIGRATION_SCREEN_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_CHROMEOS_LOGIN_ENCRYPTION_MIGRATION_SCREEN_HANDLER_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 49 matching lines @@
   // WebUIMessageHandler implementation:
   void RegisterMessages() override;
 
   // PowerManagerClient::Observer implementation:
   void PowerChanged(const power_manager::PowerSupplyProperties& proto) override;
 
   // Handlers for JS API callbacks.
   void HandleStartMigration();
   void HandleSkipMigration();
   void HandleRequestRestart();
+  void HandleRequestRestartOnFailure();
   void HandleOpenFeedbackDialog();
 
   // Updates UI state.
   void UpdateUIState(UIState state);
 
   void CheckAvailableStorage();
   void OnGetAvailableStorage(int64_t size);
   void WaitBatteryAndMigrate();
   void StartMigration();
   void OnMountExistingVault(bool success,
@@ skipping 45 matching lines @@
   std::unique_ptr<LoginFeedback> login_feedback_;
 
   base::WeakPtrFactory<EncryptionMigrationScreenHandler> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(EncryptionMigrationScreenHandler);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_UI_WEBUI_CHROMEOS_LOGIN_ENCRYPTION_MIGRATION_SCREEN_HANDLER_H_