[DevTools] Turn WebInspector.Panel into a web component.

third_party/WebKit/Source/devtools/front_end/timeline/TimelinePanel.js

Index: third_party/WebKit/Source/devtools/front_end/timeline/TimelinePanel.js
diff --git a/third_party/WebKit/Source/devtools/front_end/timeline/TimelinePanel.js b/third_party/WebKit/Source/devtools/front_end/timeline/TimelinePanel.js
index b1aaaf7c288103d53a95c088e362d60b376de11e..889d0aa1eb3e1c4a5555c67cc1aa9ebe5883a1f7 100644
--- a/third_party/WebKit/Source/devtools/front_end/timeline/TimelinePanel.js
+++ b/third_party/WebKit/Source/devtools/front_end/timeline/TimelinePanel.js
@@ -40,8 +40,8 @@ WebInspector.TimelinePanel = function()
 {
     WebInspector.Panel.call(this, "timeline");
     this.registerRequiredCSS("timeline/timelinePanel.css");
-    this.element.addEventListener("contextmenu", this._contextMenu.bind(this), false);
-    this._dropTarget = new WebInspector.DropTarget(this.element, [WebInspector.DropTarget.Types.Files, WebInspector.DropTarget.Types.URIList], WebInspector.UIString("Drop timeline file or URL here"), this._handleDrop.bind(this));
+    this.contentElement.addEventListener("contextmenu", this._contextMenu.bind(this), false);
+    this._dropTarget = new WebInspector.DropTarget(this.contentElement, [WebInspector.DropTarget.Types.Files, WebInspector.DropTarget.Types.URIList], WebInspector.UIString("Drop timeline file or URL here"), this._handleDrop.bind(this));
 
     this._state = WebInspector.TimelinePanel.State.Idle;
     this._detailsLinkifier = new WebInspector.Linkifier();
@@ -77,11 +77,11 @@ WebInspector.TimelinePanel = function()
     this._captureLayersAndPicturesSetting = WebInspector.settings.createSetting("timelineCaptureLayersAndPictures", false);
     this._captureFilmStripSetting = WebInspector.settings.createSetting("timelineCaptureFilmStrip", false);
 
-    this._panelToolbar = new WebInspector.Toolbar("", this.element);
+    this._panelToolbar = new WebInspector.Toolbar("", this.contentElement);
     this._createToolbarItems();
 
     var timelinePane = new WebInspector.VBox();
-    timelinePane.show(this.element);
+    timelinePane.show(this.contentElement);
     var topPaneElement = timelinePane.element.createChild("div", "hbox");
     topPaneElement.id = "timeline-overview-panel";
 
@@ -452,7 +452,7 @@ WebInspector.TimelinePanel.prototype = {
         if (this._fileSelectorElement)
             this._fileSelectorElement.remove();
         this._fileSelectorElement = WebInspector.createFileSelectorElement(this._loadFromFile.bind(this));
-        this.element.appendChild(this._fileSelectorElement);
+        this.contentElement.appendChild(this._fileSelectorElement);
     },
 
     /**