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

third_party/WebKit/Source/devtools/front_end/sources/SourcesPanel.js

Index: third_party/WebKit/Source/devtools/front_end/sources/SourcesPanel.js
diff --git a/third_party/WebKit/Source/devtools/front_end/sources/SourcesPanel.js b/third_party/WebKit/Source/devtools/front_end/sources/SourcesPanel.js
index c02ea12216eda0fd8c6b6d96b84fa775492dacdb..2dcbd8685f856dcfc8b9418a707739046fb14d84 100644
--- a/third_party/WebKit/Source/devtools/front_end/sources/SourcesPanel.js
+++ b/third_party/WebKit/Source/devtools/front_end/sources/SourcesPanel.js
@@ -36,7 +36,7 @@ WebInspector.SourcesPanel = function()
     WebInspector.Panel.call(this, "sources");
     WebInspector.SourcesPanel._instance = this;
     this.registerRequiredCSS("sources/sourcesPanel.css");
-    new WebInspector.DropTarget(this.element, [WebInspector.DropTarget.Types.Files], WebInspector.UIString("Drop workspace folder here"), this._handleDrop.bind(this));
+    new WebInspector.DropTarget(this.contentElement, [WebInspector.DropTarget.Types.Files], WebInspector.UIString("Drop workspace folder here"), this._handleDrop.bind(this));
 
     this._workspace = WebInspector.workspace;
     this._networkMapping = WebInspector.networkMapping;
@@ -54,7 +54,7 @@ WebInspector.SourcesPanel = function()
     const initialDebugSidebarWidth = 225;
     this._splitWidget = new WebInspector.SplitWidget(true, true, "sourcesPanelSplitViewState", initialDebugSidebarWidth);
     this._splitWidget.enableShowModeSaving();
-    this._splitWidget.show(this.element);
+    this._splitWidget.show(this.contentElement);
 
     // Create scripts navigator
     const initialNavigatorWidth = 225;
@@ -228,7 +228,7 @@ WebInspector.SourcesPanel.prototype = {
     onResize: function()
     {
         if (WebInspector.moduleSetting("sidebarPosition").get() === "auto")
-            this.element.window().requestAnimationFrame(this._updateSidebarPosition.bind(this));  // Do not force layout.
+            this.contentElement.window().requestAnimationFrame(this._updateSidebarPosition.bind(this));  // Do not force layout.
     },
 
     /**