Object properties with values of Symbol type should not be expandable.

Source/devtools/front_end/components/ObjectPropertiesSection.js

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2009 Joseph Pecoraro
  *
  * 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 225 matching lines @@
             if (this.property.value.type === "object" && this.property.value.subtype === "node" && this.property.value.description) {
                 WebInspector.DOMPresentationUtils.createSpansForNodeTitle(this.valueElement, this.property.value.description);
                 this.valueElement.addEventListener("mousemove", this._mouseMove.bind(this, this.property.value), false);
                 this.valueElement.addEventListener("mouseout", this._mouseOut.bind(this, this.property.value), false);
             } else {
                 this.valueElement.title = description || "";
             }
 
             this.listItemElement.removeChildren();
 
-            this.hasChildren = this.property.value.hasChildren && !this.property.wasThrown;
+            this.hasChildren = this.property.value.hasChildren && !this.property.wasThrown && !(this.property.value.type === "symbol");

[aandrey, 2014/06/17 10:36:33]

this.property.value.hasChildren should be false for symbols

         } else {
             if (this.property.getter) {
                 this.valueElement = WebInspector.ObjectPropertyTreeElement.createRemoteObjectAccessorPropertySpan(this.property.parentObject, [this.property.name], this._onInvokeGetterClick.bind(this));
             } else {
                 this.valueElement = document.createElement("span");
                 this.valueElement.className = "console-formatted-undefined";
                 this.valueElement.textContent = WebInspector.UIString("<unreadable>");
                 this.valueElement.title = WebInspector.UIString("No property getter");
             }
         }
@@ skipping 742 matching lines @@
 {
     WebInspector.TextPrompt.call(this, WebInspector.ExecutionContextSelector.completionsForTextPromptInCurrentContext);
     this.setSuggestBoxEnabled(true);
     if (renderAsBlock)
         this.renderAsBlock();
 }
 
 WebInspector.ObjectPropertyPrompt.prototype = {
     __proto__: WebInspector.TextPrompt.prototype
 }