DevTools: migrate sidebar pane's titleElement to use Toolbar.

Source/devtools/front_end/audits/auditsPanel.css

 /*
  * Copyright (C) 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 86 matching lines @@
 }
 
 .audit-launcher-view input[type="checkbox"] {
     margin-left: 0;
     height: 14px;
     width: 14px;
 }
 
 .audit-result-view {
     overflow: auto;
-    display: none;
-}
-
-.audit-result-view.visible {
     display: block;
     flex: auto;
 }
 
 .audit-result-tree {
     margin: 0 0 3px;
 }
 
 .audit-launcher-view .progress-indicator {
     display: inline-block;
 }
 
 .resource-url {
     float: right;
     text-align: right;
     max-width: 100%;
     margin-left: 4px;
 }