DevTools: Added ARIA roles & states to treeoutline

third_party/WebKit/Source/devtools/front_end/elements/elementsTreeOutline.css

 /*
  * Copyright (c) 2014 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.
  */
 
 .elements-disclosure {
     width: 100%;
     display: inline-block;
     line-height: normal;
@@ skipping 31 matching lines @@
 }
 
 .elements-disclosure li.parent::before {
     box-sizing: border-box;
 }
 
 .elements-disclosure li.parent::before {
     -webkit-user-select: none;
     -webkit-mask-image: url(Images/treeoutlineTriangles.png);
     -webkit-mask-size: 32px 24px;
-    content: "aa";
+    content: '\00a0\00a0';
     color: transparent;
     text-shadow: none;
     margin-right: -3px;
 }
 
 .elements-disclosure li.always-parent::before {
     visibility: hidden;
 }
 
 @media (-webkit-min-device-pixel-ratio: 1.1) {
@@ skipping 293 matching lines @@
     border-color: hsla(0,0%,0%,0.1);
 }
 
 .elements-tree-outline ol.shadow-root {
     border-color: hsla(0,0%,80%,1);
 }
 
 li.selected:not(.always-parent) + ol.children {
     border-color: hsla(216,68%,80%,1) !important;
 }