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

chrome/test/data/webui/cr_elements/cr_dialog_test.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.
+
+suite('cr-dialog', function() {
+  /** @type {HTMLDialogElement} */ var dialog;
+  /** @type {HTMLElement} */ var title;
+
+  setup(function() {
+    PolymerTest.clearBody();

[dpapad, 2017/02/23 18:28:35]

Nit: You could also do what we do at
https://cs.chromium.org/chromium/src/chrome/test/data/webui/cr_elements/cr_ac...
instead of programmatically creating the elements to be tested. It seems more
readable to me.

[Dan Beam, 2017/02/24 05:43:09]

Done.

+
+    title = document.createElement('div');
+    title.classList.add('title');
+    title.textContent = 'An Amazing Title!';
+
+    dialog = document.createElement('dialog', 'cr-dialog');
+    dialog.appendChild(title);
+    document.body.appendChild(dialog);
+  });
+
+  test('focuses title on show', function() {
+    assertNotEquals(document.activeElement, title);
+    dialog.showModal();
+    expectEquals(title.tabIndex, -1);
+    expectEquals(document.activeElement, title);

[dpapad, 2017/02/23 18:28:35]

Can we add one more test for a dialog that has an <input> element with autofocus
and check that the autofocus wins?

[Dan Beam, 2017/02/24 05:43:09]

Done.

+  });
+});