cros: Add UMA metrics in encryption migration UI.

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 95 matching lines @@
   // True if the system should resume the previous incomplete migration.
   bool should_resume_ = false;
 
   // The current battery level.
   double current_battery_percent_ = 0.0;
 
   // True if the migration should start immediately once the battery level gets
   // sufficient.
   bool should_migrate_on_enough_battery_ = false;
 
+  // The battery level at the timing that the migration starts.
+  double initial_battery_percent_ = 0.0;
+
   std::unique_ptr<device::PowerSaveBlocker> power_save_blocker_;
 
   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_