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

Source/devtools/front_end/sources/ServiceWorkersSidebarPane.js

 // Copyright (c) 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.
 
 /**
  * @constructor
  * @extends {WebInspector.SidebarPane}
  * @implements {WebInspector.TargetManager.Observer}
  */
 WebInspector.ServiceWorkersSidebarPane = function()
 {
     WebInspector.SidebarPane.call(this, WebInspector.UIString("\u2699 Service Workers"));
     this.registerRequiredCSS("sources/serviceWorkersSidebar.css");
+    this._bodyElement = this.element.createChild("div", "vbox");
     this.setVisible(false);
 
     /** @type {?WebInspector.ServiceWorkerManager} */
     this._manager = null;
     WebInspector.targetManager.observeTargets(this, WebInspector.Target.Type.Page);
     this._placeholderElement = createElementWithClass("div", "info");
     this._placeholderElement.textContent = WebInspector.UIString("No service workers control this page");
 }
 
 WebInspector.ServiceWorkersSidebarPane.prototype = {
@@ skipping 16 matching lines @@
      */
     targetRemoved: function(target)
     {
         target.serviceWorkerManager.removeEventListener(WebInspector.ServiceWorkerManager.Events.WorkersUpdated, this._update, this);
         this._updateVisibility();
     },
 
     _update: function()
     {
         this._updateVisibility();
-        this.bodyElement.removeChildren();
+        this._bodyElement.removeChildren();
 
         if (!this.isShowing() || !this._manager)
             return;
 
         if (!this._manager.hasWorkers()) {
-            this.bodyElement.appendChild(this._placeholderElement);
+            this._bodyElement.appendChild(this._placeholderElement);
             return;
         }
 
         for (var worker of this._manager.workers()) {
-            var workerElement = this.bodyElement.createChild("div", "service-worker");
+            var workerElement = this._bodyElement.createChild("div", "service-worker");
             var leftBox = workerElement.createChild("div", "vbox flex-auto");
             leftBox.appendChild(WebInspector.linkifyURLAsNode(worker.url(), worker.name()));
             var scopeElement = leftBox.createChild("span", "service-worker-scope");
             scopeElement.textContent = worker.scope();
             scopeElement.title = worker.scope();
             workerElement.appendChild(createTextButton(WebInspector.UIString("Unregister"), worker.stop.bind(worker)));
         }
     },
 
     _updateVisibility: function()
     {
         this._wasVisibleAtLeastOnce = this._wasVisibleAtLeastOnce || !!this._manager && this._manager.hasWorkers();
         this.setVisible(this._wasVisibleAtLeastOnce);
     },
 
     wasShown: function()
     {
         this._update();
     },
 
     __proto__: WebInspector.SidebarPane.prototype
 }