DevTools: a11y test for Performance tool landing page

This change only adds an axe test for performance tool landing page

Bug: 963183
Change-Id: I583e36a24d53fbb77c495c716876165deba66151
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1699133Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Junyi Xiao <juxiao@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#697266}

third_party/blink/web_tests/http/tests/devtools/a11y-axe-core/performance/landing-page-a11y-test-expected.txt

+Tests accessibility in Performance landing page using the axe-core linter.
+aXe violations: []
+
+

third_party/blink/web_tests/http/tests/devtools/a11y-axe-core/performance/landing-page-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() {
+  TestRunner.addResult('Tests accessibility in Performance landing page using the axe-core linter.');
+
+  await TestRunner.loadModule('axe_core_test_runner');
+  const view = 'timeline';
+  await UI.viewManager.showView(view);
+  const widget = await UI.viewManager.view(view).widget();
+  await AxeCoreTestRunner.runValidation(widget.element);
+
+  TestRunner.completeTest();
+})();
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