DevTools: Add toolbar bottom separator to timeline tree views.

third_party/WebKit/Source/devtools/front_end/timeline/timelinePanel.css

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Anthony Ricaud <rik@webkit.org>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 502 matching lines @@
 .timeline-overview-popover .frame .thumbnail img {
     max-width: 300px;
     max-height: 500px;
 }
 
 .timeline-tree-view {
     display: flex;
     overflow: hidden;
 }
 
-.timeline-tree-view > .toolbar {
+.timeline-tree-view .toolbar {
     border-bottom: 1px solid #dadada;
 }
 
 .timeline-tree-view .data-grid {
     border: none;
     flex: auto;
 }
 
 .timeline-tree-view .data-grid .data-container {
     overflow-y: scroll;
@@ skipping 141 matching lines @@
 
 .timeline-landing-warning-close {
     float: right;
     margin-top: -10px;
     margin-right: -13px;
 }
 
 .timeline-landing-warning span[is=ui-icon] {
     margin: -8px;
 }