DevTools: Migrate from -webkit-user-modify to contenteditable

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 166 matching lines @@
 .CodeMirror pre {
     padding: 0;
 }
 
 button, input, select {
   font-family: inherit;
   font-size: inherit;
 }
 
 .editing {
-    -webkit-user-select: text;
     box-shadow: 0 0 0 1px rgba(0, 0, 0, 0.2),
                 0 2px 4px rgba(0, 0, 0, 0.2),
                 0 2px 6px rgba(0, 0, 0, 0.1);
     background-color: white;
-    -webkit-user-modify: read-write-plaintext-only;
     text-overflow: clip !important;
     padding-left: 2px;
     margin-left: -2px;
     padding-right: 2px;
     margin-right: -2px;
     margin-bottom: -1px;
     padding-bottom: 1px;
     opacity: 1.0 !important;
 }
 
@@ skipping 145 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;
 }