DevTools: migrate ComputedStyleWidget to shadow

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

 /*
- * Copyright (c) 2015 The Chromium Authors. All rights reserved.
+ * Copyright (c) 2017 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.
  */
 
-.computed-properties {
-    -webkit-user-select: text;
-    flex-shrink: 0;
-}
-
 .computed-style-property {
     display: flex;
     overflow: hidden;
     flex: auto;
 }
 
 .computed-style-property .property-name {
     min-width: 5em;
     text-overflow: ellipsis;
     overflow: hidden;
@@ skipping 89 matching lines @@
     margin-left: 4px;
 }
 
 .delimeter {
     color: transparent;
 }
 
 .delimeter::selection {
     color: transparent;
 }