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

Source/devtools/front_end/inspectorStyle.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 110 matching lines @@
 
 .error-message {
     color: red;
 }
 
 .error-input {
     background-color: rgb(220, 130, 130);
 }
 
 .panel {
-    display: none !important;
+    display: flex;
     overflow: hidden;
     position: absolute;
     top: 0;
     left: 0;
     right: 0;
     bottom: 0;
     z-index: 0;
 }
 
-.panel.visible {
-    display: flex !important;
-}
-
 iframe.extension {
     flex: auto;
     width: 100%;
     height: 100%;
 }
 
 iframe.panel.extension {
     display: block;
     height: 100%;
 }
@@ skipping 492 matching lines @@
 }
 
 body.inactive select.chrome-select,
 .chrome-select:disabled {
     background-image: -webkit-image-set(url(Images/chromeDisabledSelect.png) 1x, url(Images/chromeDisabledSelect_2x.png) 2x), linear-gradient(#f1f1f1, #f1f1f1 38%, #e6e6e6);
     border-color: rgba(80, 80, 80, 0.2);
     box-shadow: 0 1px 0 rgba(80, 80, 80, 0.08),
     inset 0 1px 2px rgba(255, 255, 255, 0.75);
     color: #aaa;
 }