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',
+
+  properties: {
+    /**
+     * True if the dialog is currently hidden.
+     * @private {boolean}
+     */
+    dialogHidden_: {
+      type: Boolean,
+      value: true
+    }
+  },
+
+  /**
+   * Opens the dialog.
+   */
+  open: function() {
+    this.dialogHidden_ = false;
+
+    this.async(function() {
+      this.$$('paper-icon-button').focus();
+    }.bind(this));
+  },
+
+  /**
+   * Closes the popup.
+   */
+  close: function() {
+    this.dialogHidden_ = true;
+  }
+});