MD User Manager: Refactors existing dialogs in User Manager into <user-manager-dialog>

chrome/browser/resources/md_user_manager/user_manager_dialog.js

+// Copyright 2016 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 'user-manager-dialog' is a modal dialog for the user manager.
+ */
+Polymer({
+  is: 'user-manager-dialog',
+
+  behaviors: [Polymer.PaperDialogBehavior],
+
+  properties: {
+    /** @override */
+    noCancelOnOutsideClick: {
+      type: Boolean,
+      value: true
+    },
+
+    /** @override */
+    withBackdrop: {
+      type: Boolean,
+      value: true
+    },
+
+    /**
+     * The first node that can receive focus.
+     * @type {Node}
+     */
+    firstFocusableNode: {
+      type: Object,
+      value: function() { return this.$.close; },
+      observer: 'firstFocusableNodeChanged_'
+    },
+
+    /**
+     * The last node that can receive focus.
+     * @type {Node}
+     */
+    lastFocusableNode: {
+      type: Object,
+      value: function() { return this.$.close; },
+      observer: 'lastFocusableNodeChanged_'
+    }
+  },
+
+  /**
+   * Returns the first and the last focusable elements in order to wrap the
+   * focus for the dialog in Polymer.PaperDialogBehavior.
+   * @override
+   * @type {Array<Node>}
+   */
+  get _focusableNodes() {
+    return [this.firstFocusableNode, this.lastFocusableNode];
+  },
+
+  /**
+   * Observer for firstFocusableNode. Updates __firstFocusableNode in
+   * Polymer.PaperDialogBehavior.
+   */
+  firstFocusableNodeChanged_: function(newValue) {
+    this.__firstFocusableNode = newValue;

[Moe, 2016/06/03 21:51:50]

__firstFocusableNode is not part of PaperDialogBehavior's paper dialog. But this
is the only way I could come up with to update the focusable nodes *after* the
dialog opens. Same thing below.

+  },
+
+  /**
+   * Observer for lastFocusableNodeChanged_. Updates __lastFocusableNode in
+   * Polymer.PaperDialogBehavior.
+   */
+  lastFocusableNodeChanged_: function(newValue) {
+    this.__lastFocusableNode = newValue;
+  }
+});