2nd arg of document.createElement should be an object

third_party/WebKit/Source/core/dom/Document.idl

 /*
  * Copyright (C) 2006, 2007, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006, 2007 Samuel Weinig <sam@webkit.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 158 matching lines @@
                       [Default=Undefined] optional unrestricted float rotationAngle,
                       [Default=Undefined] optional unrestricted float force);
     [RuntimeEnabled=Touch] TouchList createTouchList(Touch... touches);
 
     // Custom Elements
     // http://w3c.github.io/webcomponents/spec/custom/#extensions-to-document-interface-to-register
     // FIXME: The registerElement return type should be Function.
     [CallWith=ScriptState, CustomElementCallbacks, RaisesException, MeasureAs=DocumentRegisterElement] CustomElementConstructor registerElement(DOMString type, optional ElementRegistrationOptions options);
     // http://w3c.github.io/webcomponents/spec/custom/#extensions-to-document-interface-to-instantiate
     // FIXME: The typeExtension arguments should not be nullable.
-    [CustomElementCallbacks, PerWorldBindings, RaisesException] Element createElement(DOMString localName, DOMString? typeExtension);
-    [CustomElementCallbacks, RaisesException] Element createElementNS(DOMString? namespaceURI, DOMString qualifiedName, DOMString? typeExtension);
+    [CustomElementCallbacks, PerWorldBindings, RaisesException] Element createElement(DOMString localName, (DOMString or Dictionary)? options);
+    [CustomElementCallbacks, RaisesException] Element createElementNS(DOMString? namespaceURI, DOMString qualifiedName, (DOMString or Dictionary)? options);
 
     // Page Visibility
     // http://www.w3.org/TR/page-visibility/#sec-document-interface
     readonly attribute boolean hidden;
     readonly attribute VisibilityState visibilityState;
 
     // CORS and RFC1918
     // https://mikewest.github.io/cors-rfc1918/#feature-detect
     [RuntimeEnabled=CorsRFC1918, ImplementedAs=addressSpaceForBindings] readonly attribute AddressSpace addressSpace;
 
@@ skipping 17 matching lines @@
     [RuntimeEnabled=ExperimentalContentSecurityPolicyFeatures] attribute EventHandler onsecuritypolicyviolation;
     attribute EventHandler onselectionchange;
     attribute EventHandler onselectstart;
     attribute EventHandler onwheel;
 };
 
 Document implements GlobalEventHandlers;
 Document implements ParentNode;
 Document implements NonElementParentNode;
 Document implements DocumentOrShadowRoot;