Implement a basic UI flow for cryptohome encryption migration.

chrome/browser/resources/chromeos/login/encryption_migration.js

+// 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.
+
+/**
+ * @fileoverview Polymer element for displaying encryption migration screen.
+ */
+
+/**
+ * Enum for the UI states corresponding to sub steps inside migration screen.
+ * These values must be kept in sync with
+ * EncryptionMigrationScreenHandler::UIState in C++ code.
+ * @enum {number}
+ */
+var EncryptionMigrationUIState = {
+  INITIAL: 0,
+  MIGRATING: 1,
+  MIGRATION_SUCCEEDED: 2,
+  MIGRATION_FAILED: 3
+};
+
+Polymer({
+  is: 'encryption-migration',
+
+  properties: {
+    /**
+     * Current UI state which corresponds to a sub step in migration process.
+     * @type {EncryptionMigrationUIState}
+     */
+    uiState: {
+      type: Number,
+      value: 0
+    },
+
+    /**
+     * Current migration progress in range [0, 1]. Negative value means that
+     * the progress is unknown.
+     */
+    progress: {
+      type: Number,
+      value: -1
+    },
+  },
+
+  /**
+   * Returns true if the migration is in initial state.
+   * @param {EncryptionMigrationUIState} state Current UI state
+   * @private
+   */
+  isInitial_: function(state) {
+    return state == EncryptionMigrationUIState.INITIAL;
+  },
+
+  /**
+   * Returns true if the migration is in progress.
+   * @param {EncryptionMigrationUIState} state Current UI state
+   * @private
+   */
+  isMigrating_: function(state) {
+    return state == EncryptionMigrationUIState.MIGRATING;
+  },
+
+  /**
+   * Returns true if the migration is finished successfully.
+   * @param {EncryptionMigrationUIState} state Current UI state
+   * @private
+   */
+  isMigrationSucceeded_: function(state) {
+    return state == EncryptionMigrationUIState.MIGRATION_SUCCEEDED;
+  },
+
+  /**
+   * Returns true if the migration failed.
+   * @param {EncryptionMigrationUIState} state Current UI state
+   * @private
+   */
+  isMigrationFailed_: function(state) {

[xiyuan, 2017/03/30 17:55:39]

Where is the UI for this state?

[fukino, 2017/03/31 02:29:52]

Done. I added a view for the failure. Thanks!

+    return state == EncryptionMigrationUIState.MIGRATION_FAILED;
+  },
+
+  /**
+   * Returns true if the current migration progress is unknown.
+   * @param {number} progress
+   * @private
+   */
+  isProgressIndeterminate_: function(progress) {
+    return progress < 0;
+  },
+
+  /**
+   * Handles tap on UPGRADE button.
+   * @private
+   */
+  onUpgrade_: function() {
+    this.fire('upgrade');
+  },
+
+  /**
+   * Handles tap on SKIP button.
+   * @private
+   */
+  onSkip_: function() {
+    this.fire('skip');
+  },
+
+  /**
+   * Handles tap on RESTART button.
+   * @private
+   */
+  onRestart_: function() {
+    this.fire('restart');
+  },
+});