DevTools: Fix "toolbox" app startup in the debug_devtools mode

Source/devtools/front_end/toolbox_bootstrap/Toolbox.js

 // Copyright 2014 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.
 
-function windowLoaded()
-{
-    window.removeEventListener("DOMContentLoaded", windowLoaded, false);
-    new WebInspector.Toolbox();
-}
-window.addEventListener("DOMContentLoaded", windowLoaded, false);
-
 /**
  * @constructor
  */
 WebInspector.Toolbox = function()
 {
     if (!window.opener)
         return;
 
     WebInspector.zoomManager = new WebInspector.ZoomManager(window.opener.InspectorFrontendHost);
     WebInspector.overridesSupport = window.opener.WebInspector.overridesSupport;
@@ skipping 11 matching lines @@
     var inspectedPagePlaceholder = new WebInspector.InspectedPagePlaceholder();
     this._responsiveDesignView = new WebInspector.ResponsiveDesignView(inspectedPagePlaceholder);
     this._responsiveDesignView.show(rootView.element);
     rootView.attachToBody();
     delegate.toolboxLoaded(this._responsiveDesignView, inspectedPagePlaceholder);
 }
 
 // FIXME: This stub is invoked from the backend and should be removed
 // once we migrate to the "pull" model for extensions retrieval.
 WebInspector.addExtensions = function() {}
+
+function windowLoaded()
+{
+    window.removeEventListener("DOMContentLoaded", windowLoaded, false);
+    new WebInspector.Toolbox();
+}
+
+if (document.readyState === "complete")
+    new WebInspector.Toolbox();
+else
+    window.addEventListener("DOMContentLoaded", windowLoaded, false);