MD Settings: Don't auto-close navigable dialogs on popstate.

ui/webui/resources/cr_elements/cr_dialog/cr_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 'cr-dialog' is a component for showing a modal dialog. If the
  * dialog is closed via close(), a 'close' event is fired. If the dialog is
  * canceled via cancel(), a 'cancel' event is fired followed by a 'close' event.
  * Additionally clients can inspect the dialog's |returnValue| property inside
  * the 'close' event listener to determine whether it was canceled or just
  * closed, where a truthy value means success, and a falsy value means it was
  * canceled.
  */
 Polymer({
   is: 'cr-dialog',
   extends: 'dialog',
 
+  properties: {
+    /**
+     * True if the dialog should remain open on 'popstate' events. This is used
+     * for navigable dialogs that have their separate navigation handling code.
+     */
+    ignorePopstate: {
+      type: Boolean,
+      value: false,
+    },
+  },
+
   /** @override */
-  created: function() {
+  ready: function() {
     // If the active history entry changes (i.e. user clicks back button),
     // all open dialogs should be cancelled.
     window.addEventListener('popstate', function() {
-      if (this.open)
+      if (!this.ignorePopstate && this.open)
         this.cancel();
     }.bind(this));
   },
 
   cancel: function() {
     this.fire('cancel');
     HTMLDialogElement.prototype.close.call(this, '');
   },
 
   /**
    * @param {string=} opt_returnValue
    * @override
    */
   close: function(opt_returnValue) {
     HTMLDialogElement.prototype.close.call(this, 'success');
   },
 
   /** @return {!PaperIconButtonElement} */
   getCloseButton: function() {
     return this.$.close;
   },
 });