[DevTools] Migrate RequestHeadersView to TreeOutlineInShadow.

third_party/WebKit/Source/devtools/front_end/network/requestHeadersTree.css

+/*
+ * Copyright 2016 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.
+ */
+
+.tree-outline > ol {
+    padding-bottom: 5px;
+}
+
+.tree-outline > .parent {
+    -webkit-user-select: none;
+    font-weight: bold;
+    color: #616161;
+    margin-top: -1px;
+    height: 20px;
+    border-top: solid 1px #e0e0e0;
+    display: flex;
+    align-items: center;
+}
+
+.tree-outline li {
+    display: block;
+}
+
+.tree-outline li:not(.parent) {
+    margin-left: 10px;
+}
+
+.tree-outline li:not(.parent)::before {
+    display: none;
+}
+
+.tree-outline .caution {
+    margin-left: 4px;
+    display: inline-block;
+    font-weight: bold;
+}
+
+.tree-outline li.expanded .header-count {
+    display: none;
+}
+
+.tree-outline li .header-toggle {
+    display: none;
+}
+
+.tree-outline li .status-from-cache {
+    color: gray;
+}
+
+.tree-outline li.expanded .header-toggle {
+    display: inline;
+    margin-left: 30px;
+    font-weight: normal;
+    color: rgb(45%, 45%, 45%);
+}
+
+.tree-outline li .header-toggle:hover {
+    color: rgb(20%, 20%, 45%);
+    cursor: pointer;
+}
+
+.tree-outline .header-name {
+    color: rgb(33%, 33%, 33%);
+    display: inline-block;
+    margin-right: 0.5em;
+    font-weight: bold;
+    vertical-align: top;
+    white-space: pre-wrap;
+}
+
+.tree-outline .header-value {
+    display: inline;
+    margin-right: 1em;
+    white-space: pre-wrap;
+    word-break: break-all;
+    margin-top: 1px;
+}
+
+.tree-outline .empty-request-header {
+    color: rgba(33%, 33%, 33%, 0.5);
+}