DevTools: add axe-core test for the WebAudio tool

Bug: 963183
Change-Id: I16c95430821e329433334a9d6515b9c3fc555f20
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1711061Reviewed-by: Erik Luo <luoe@chromium.org>
Commit-Queue: John Emau <johnemau@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#682086}

third_party/blink/web_tests/http/tests/devtools/a11y-axe-core/web-audio-a11y-test-expected.txt

+Tests accessibility in the web audio tool using the axe-core linter.
+aXe violations: []
+
+

third_party/blink/web_tests/http/tests/devtools/a11y-axe-core/web-audio-a11y-test.js

+// Copyright 2019 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.
+
+(async function() {
+  await TestRunner.loadModule('axe_core_test_runner');
+  TestRunner.addResult(
+      'Tests accessibility in the web audio tool using the axe-core linter.');
+
+  await UI.viewManager.showView('web-audio');
+  const widget = await UI.viewManager.view('web-audio').widget();
+
+  await AxeCoreTestRunner.runValidation(widget.element);
+  TestRunner.completeTest();
+})();
+