DevTools: rely upon shouldHideOnDetach when considering re-layout of elements and sources panels.

Source/devtools/front_end/extensions/ExtensionView.js

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 21 matching lines @@
  * @constructor
  * @extends {WebInspector.Widget}
  * @param {!WebInspector.ExtensionServer} server
  * @param {string} id
  * @param {string} src
  * @param {string} className
  */
 WebInspector.ExtensionView = function(server, id, src, className)
 {
     WebInspector.Widget.call(this);
+    this.setHideOnDetach();
     this.element.className = "vbox flex-auto"; // Override
 
     this._server = server;
     this._id = id;
     this._iframe = createElement("iframe");
     this._iframe.addEventListener("load", this._onLoad.bind(this), false);
     this._iframe.src = src;
     this._iframe.className = className;
     this.setDefaultFocusedElement(this._iframe);
 
@@ skipping 44 matching lines @@
         this._server.notifyViewShown(this._id);
     },
 
     willHide: function()
     {
         this._server.notifyViewHidden(this._id);
     },
 
     __proto__: WebInspector.VBox.prototype
 }