Devtools: Re-enable TreeOutline Tests and add aXe Test

This CL re-enables and rebaselines 2 tests that were disabled to land
an accessibility change to devtools treeoutlines. It additionally adds
an aXe test to prevent regressions. This effectively reverts
https://chromium-review.googlesource.com/c/chromium/src/+/1962600

Related devtools change:
https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/1960952

Bug: 1033213
Change-Id: Ieaefa3b18b294073af1a16cf63f9d0014f6f5bb1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1976495Reviewed-by: Lorne Mitchell <lomitch@microsoft.com>
Commit-Queue: Brandon Goddard <brgoddar@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#726489}

third_party/blink/web_tests/TestExpectations

@@ -6066,10 +6066,6 @@ crbug.com/1006759 inspector-protocol/heap-profiler/heap-snapshot-with-event-list
 crbug.com/1006759 inspector-protocol/heap-profiler/heap-snapshot-with-multiple-retainers.js [ Pass Failure ]
 crbug.com/1006759 inspector-protocol/heap-profiler/heap-snapshot-with-no-detached-iframe.js [ Pass Failure ]
 
-# Temporarily disabled for landing changes to treeoutline in DevTools
-crbug.com/1033213 http/tests/devtools/security/interstitial-sidebar.js [ Pass Failure ]
-crbug.com/1033213 http/tests/devtools/security/mixed-content-sidebar.js [ Pass Failure ]
-
 # Sheriff 2019-12-13
 crbug.com/1032451 [ Win7 ] virtual/webrtc-wpt-plan-b/external/wpt/webrtc/idlharness.https.window.html [ Failure ]
 crbug.com/1033852 [ Win7 ] virtual/omt-worker-fetch/external/wpt/fetch/api/idlharness.any.sharedworker.html [ Failure ]

third_party/blink/web_tests/http/tests/devtools/a11y-axe-core/application-panel/application-tree-outline-expected.txt

+Tests accessibility of Tree outline sidepane in Application Panel.
+aXe violations: []
+
+

third_party/blink/web_tests/http/tests/devtools/a11y-axe-core/application-panel/application-tree-outline.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 of Tree outline sidepane in Application Panel.');
+
+  await TestRunner.showPanel('resources');
+  const applicationSidebar = UI.panels.resources.panelSidebarElement();
+  await AxeCoreTestRunner.runValidation(applicationSidebar);
+  TestRunner.completeTest();
+})();

third_party/blink/web_tests/http/tests/devtools/security/interstitial-sidebar-expected.txt

@@ -13,7 +13,7 @@ Before interstitial is shown:
         </STYLE>
         <DIV class=tree-outline-disclosure >
             <OL class=tree-outline role=tree tabindex=-1 >
-                <LI role=treeitem class=security-main-view-sidebar-tree-item selected force-white-icons tabindex=0 >
+                <LI role=treeitem class=security-main-view-sidebar-tree-item selected force-white-icons tabindex=0 aria-selected=true >
                     <DIV class=selection fill >
                     </DIV>
                     <SPAN class=tree-element-title >
@@ -134,7 +134,7 @@ After interstitial is shown:
         </STYLE>
         <DIV class=tree-outline-disclosure >
             <OL class=tree-outline role=tree tabindex=-1 >
-                <LI role=treeitem class=security-main-view-sidebar-tree-item selected force-white-icons tabindex=0 >
+                <LI role=treeitem class=security-main-view-sidebar-tree-item selected force-white-icons tabindex=0 aria-selected=true >
                     <DIV class=selection fill >
                     </DIV>
                     <SPAN class=tree-element-title >
@@ -255,7 +255,7 @@ After interstitial is hidden:
         </STYLE>
         <DIV class=tree-outline-disclosure >
             <OL class=tree-outline role=tree tabindex=-1 >
-                <LI role=treeitem class=security-main-view-sidebar-tree-item selected force-white-icons tabindex=0 >
+                <LI role=treeitem class=security-main-view-sidebar-tree-item selected force-white-icons tabindex=0 aria-selected=true >
                     <DIV class=selection fill >
                     </DIV>
                     <SPAN class=tree-element-title >

third_party/blink/web_tests/http/tests/devtools/security/mixed-content-sidebar-expected.txt

@@ -13,7 +13,7 @@ Origin sidebar:
         </STYLE>
         <DIV class=tree-outline-disclosure >
             <OL class=tree-outline role=tree tabindex=-1 >
-                <LI role=treeitem class=security-main-view-sidebar-tree-item selected force-white-icons tabindex=0 >
+                <LI role=treeitem class=security-main-view-sidebar-tree-item selected force-white-icons tabindex=0 aria-selected=true >
                     <DIV class=selection fill >
                     </DIV>
                     <SPAN class=tree-element-title >