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

Source/devtools/front_end/console/ConsoleViewMessage.js

 /*
  * Copyright (C) 2011 Google Inc.  All rights reserved.
  * Copyright (C) 2007, 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
@@ skipping 37 matching lines @@
     /** @type {!Map.<!WebInspector.DataGrid, ?Element>} */
     this._dataGridParents = new Map();
 
     /** @type {!Object.<string, function(!WebInspector.RemoteObject, !Element, boolean=)>} */
     this._customFormatters = {
         "object": this._formatParameterAsObject,
         "array": this._formatParameterAsArray,
         "node": this._formatParameterAsNode,
         "map": this._formatParameterAsObject,
         "set": this._formatParameterAsObject,
+        "iterator": this._formatParameterAsObject,
         "string": this._formatParameterAsString
     };
 }
 
 WebInspector.ConsoleViewMessage.prototype = {
     /**
      * @return {?WebInspector.Target}
      */
     _target: function()
     {
@@ skipping 1312 matching lines @@
     {
         if (!this._wrapperElement) {
             WebInspector.ConsoleViewMessage.prototype.toMessageElement.call(this);
             this._wrapperElement.classList.toggle("collapsed", this._collapsed);
         }
         return this._wrapperElement;
     },
 
     __proto__: WebInspector.ConsoleViewMessage.prototype
 }