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

Source/devtools/front_end/inspectorStyle.css

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Anthony Ricaud <rik@webkit.org>
  *
  * 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.
@@ skipping 1107 matching lines @@
     margin-right: -6px;
 }
 
 .console-group-messages .add-attribute {
     display: none;
 }
 
 .console-formatted-object,
 .console-formatted-map,
 .console-formatted-set,
+.console-formatted-iterator,
 .console-formatted-node,
 .console-formatted-array {
     position: relative;
     display: inline-block;
     vertical-align: top;
     color: inherit;
 }
 
 .console-formatted-node:hover {
     background-color: rgba(56, 121, 217, 0.1);
 }
 
 .console-formatted-object .section,
 .console-formatted-map .section,
 .console-formatted-set .section,
+.console-formatted-iterator .section,
 .console-formatted-node .section,
 .console-formatted-array .section {
     position: static;
 }
 
 .console-formatted-object .section > .header::before {
     margin-top: 0;
 }
 
 .console-formatted-object .properties,
 .console-formatted-map .properties,
 .console-formatted-set .properties,
+.console-formatted-iterator .properties,
 .console-formatted-node .properties {
     padding-left: 0 !important;
 }
 
 .console-formatted-number,
 .console-formatted-boolean {
     color: rgb(28, 0, 207);
 }
 
 .scientific-notation-exponent {
@@ skipping 1648 matching lines @@
     font-size: 80%;
     white-space: nowrap;
     pointer-events: none;
 }
 
 .link {
     cursor: pointer;
     text-decoration: underline;
     color: rgb(17, 85, 204);
 }