Devtools UX: Add elements toolbar with breadcrumbs

Source/devtools/front_end/ui/toolbar.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.
  */
 
 :host {
     flex: none;
 }
 
@@ skipping 239 matching lines @@
 .toolbar-counter-item.toolbar-counter-item-first {
     margin-left: 0;
 }
 
 .toolbar-counter-item > div {
     margin-right: 2px;
 }
 
 .toolbar-divider {
     margin-left: 7px;
-    border-right: 1px solid #CCC;
+    border-right: 1px solid hsla(0, 0%, 0%, 0.1);
+}
+
+:host-context(.material) .toolbar-divider {
+    height: 18px;
 }
 
 .toolbar-group-label {
     margin-left: 6px;
     margin-right: 3px;
     color: #888;
 }
 
 
 /* Predefined items */
@@ skipping 227 matching lines @@
 }
 
 .playback-rate-button.toggled-on > .toolbar-button-text {
     color: rgb(66, 129, 235);
 }
 
 button.playback-rate-button {
     width: auto;
     margin-right: 10px;
 }