MD Settings: focus header when dialog shows to signal to AT what's going on

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
@@ skipping 23 matching lines @@
   /** @override */
   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.ignorePopstate && this.open)
         this.cancel();
     }.bind(this));
   },
 
+  /** @override */
+  attached: function() {
+    var title = this.getContentChildren('[select=".title"]');

[dpapad, 2017/02/24 20:46:10]

Nit(optional): Perhaps use queryEffectiveChildren instead which returns the 1st
occurrence instead of an array?

[Dan Beam, 2017/02/24 22:08:31]

that's different.  that gets all the distributed children.  i mean, it'd
probably functionally work because the first node with class="title" would
likely be in this slot and it'd be crazy to use class="title" inside of
class="body", but this is specifically looking for the first child of a specific
<content> slot

+    if (title.length)
+      title[0].tabIndex = -1;
+  },
+
   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;
   },
 });