DevTools: Show preview for ES6 MapIterator, SetIterator in console.

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 555 matching lines @@
             for (var i = 0; i < internalProperties.length; i++) {
                 if (internalProperties[i].name == "[[TargetFunction]]") {
                     hasTargetFunction = true;
                     break;
                 }
             }
         }
         if (!hasTargetFunction)
             treeElement.appendChild(new WebInspector.FunctionScopeMainTreeElement(value));
     }
-    if (value && value.type === "object" && (value.subtype === "map" || value.subtype === "set"))
+    if (value && value.type === "object" && (value.subtype === "map" || value.subtype === "set" || value.subtype === "iterator"))
         treeElement.appendChild(new WebInspector.CollectionEntriesMainTreeElement(value));
     if (internalProperties) {
         for (var i = 0; i < internalProperties.length; i++) {
             internalProperties[i].parentObject = value;
             treeElement.appendChild(new treeElementConstructor(internalProperties[i]));
         }
     }
 
     WebInspector.ObjectPropertyTreeElement._appendEmptyPlaceholderIfNeeded(treeElement, emptyPlaceholder);
 }
@@ skipping 496 matching lines @@
 {
     WebInspector.TextPrompt.call(this, WebInspector.ExecutionContextSelector.completionsForTextPromptInCurrentContext);
     this.setSuggestBoxEnabled(true);
     if (renderAsBlock)
         this.renderAsBlock();
 }
 
 WebInspector.ObjectPropertyPrompt.prototype = {
     __proto__: WebInspector.TextPrompt.prototype
 }