DevTools: migrate treeoutline from hasChildren to is/setExpandable().

Source/devtools/front_end/sources/ScopeChainSidebarPane.js

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2011 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 133 matching lines @@
             this.bodyElement.appendChild(section.element);
         }
     },
 
     /**
      * @param {!WebInspector.Event} event
      */
     _elementAttached: function(event)
     {
         var element = /** @type {!WebInspector.ObjectPropertyTreeElement} */ (event.data);
-        if (element.hasChildren && this._expandedProperties.has(this._propertyPath(element)))
+        if (element.isExpandable() && this._expandedProperties.has(this._propertyPath(element)))
             element.expand();
     },
 
     /**
      * @param {!WebInspector.Event} event
      */
     _elementExpanded: function(event)
     {
         var element = /** @type {!WebInspector.ObjectPropertyTreeElement} */ (event.data);
         this._expandedProperties.add(this._propertyPath(element));
@@ skipping 13 matching lines @@
      * @return {string}
      */
     _propertyPath: function(treeElement)
     {
         var section = treeElement.treeOutline.section;
         return section.title + ":" + (section.subtitle ? section.subtitle + ":" : "") + WebInspector.ObjectPropertyTreeElement.prototype.propertyPath.call(treeElement);
     },
 
     __proto__: WebInspector.SidebarPane.prototype
 }