Add <menuitem>, new HTMLMenuElement IDL attributes.

Source/core/css/html.css

 /*
  * The default style sheet used to render HTML.
  *
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * 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.
@@ skipping 632 matching lines @@
 
 option:-internal-spatial-navigation-focus {
     outline: black dashed 1px;
     outline-offset: -1px;
 }
 
 datalist {
     display: none
 }
 
+menuitem {

[tkent, 2014/08/11 01:58:32]

We can't add CSS rules for a runtime-enabled feature to html.css because the
rules are effective even if the feature is disabled.  Please refer to
RenderTheme::extraDefaultStyleSheet.

[pals, 2014/08/11 09:11:58]

Done.

+    display: none
+}
+
 area, param {
     display: none
 }
 
 input[type="checkbox" i] {
     -webkit-appearance: checkbox;
     box-sizing: border-box;
 }
 
 input[type="radio" i] {
@@ skipping 429 matching lines @@
 @page {
     /* FIXME: Define the right default values for page properties. */
     size: auto;
     margin: auto;
     padding: 0px;
     border-width: 0px;
 }
 
 /* noscript is handled internally, as it depends on settings. */