[DevTools] Migrate RequestHeadersView to TreeOutlineInShadow.

third_party/WebKit/Source/devtools/front_end/ui/treeoutline.css

 /*
  * Copyright 2015 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.
  */
 
 :host {
     flex: 1 1;
     padding: 2px 0 0 0;
 }
@@ skipping 107 matching lines @@
     -webkit-mask-position: -20px -96px;
 }
 
 .tree-outline ol.children {
     display: none;
 }
 
 .tree-outline ol.children.expanded {
     display: block;
 }
+
+.tree-outline.tree-outline-dense li {
+    margin-top: 1px;
+    min-height: 12px;
+}
+
+.tree-outline.tree-outline-dense li.parent {
+    margin-top: 0;
+}
+
+.tree-outline.tree-outline-dense li.parent::before {
+    top: 0;
+}
+
+.tree-outline.tree-outline-dense ol {
+    padding-left: 10px;
+}