Add a screen to migrate filesystem encryption from eCryptfs to ext4 crypto.

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

+// 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.
+
+#include "chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.h"
+
+namespace {
+
+constexpr char kJsScreenPath[] = "login.EncryptionMigrationScreen";
+
+}  // namespace
+
+namespace chromeos {
+
+EncryptionMigrationScreenHandler::EncryptionMigrationScreenHandler()
+    : BaseScreenHandler(kScreenId) {
+  set_call_js_prefix(kJsScreenPath);
+}
+
+EncryptionMigrationScreenHandler::~EncryptionMigrationScreenHandler() {
+  if (delegate_)
+    delegate_->OnViewDestroyed(this);
+}
+
+void EncryptionMigrationScreenHandler::Show() {
+  if (!page_is_ready() || !delegate_) {
+    show_on_init_ = true;
+    return;
+  }
+  ShowScreen(kScreenId);
+}
+
+void EncryptionMigrationScreenHandler::Hide() {
+  show_on_init_ = false;
+}
+
+void EncryptionMigrationScreenHandler::SetDelegate(Delegate* delegate) {
+  delegate_ = delegate;
+  if (page_is_ready())
+    Initialize();
+}
+
+void EncryptionMigrationScreenHandler::DeclareLocalizedValues(
+    ::login::LocalizedValuesBuilder* builder) {}
+
+void EncryptionMigrationScreenHandler::Initialize() {
+  if (!page_is_ready() || !delegate_)
+    return;
+
+  if (show_on_init_) {
+    Show();
+    show_on_init_ = false;
+  }
+}
+
+}  // namespace chromeos