Remove iframe@seamless

Source/core/html/HTMLIFrameElement.idl

 /*
  * Copyright (C) 2006, 2007, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  *
  * 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,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 interface HTMLIFrameElement : HTMLElement {
     [Reflect] attribute DOMString align;
     [Reflect] attribute DOMString frameBorder;
     [Reflect] attribute DOMString height;
     [Reflect, URL] attribute DOMString longDesc;
     [Reflect, TreatNullAs=NullString] attribute DOMString marginHeight;
     [Reflect, TreatNullAs=NullString] attribute DOMString marginWidth;
     [Reflect] attribute DOMString name;
     [Reflect, TreatNullAs=NullString] attribute DOMString sandbox;
-    [Reflect, RuntimeEnabled=SeamlessIFrames] attribute boolean seamless;
     [Reflect] attribute DOMString scrolling;
     [Reflect, URL, PerWorldBindings, ActivityLogging=SetterForIsolatedWorlds] attribute DOMString src;
     [Reflect] attribute DOMString srcdoc;
     [Reflect] attribute DOMString width;
 
     // Introduced in DOM Level 2:
     [CheckSecurity=Node] readonly attribute Document contentDocument;
 
     // Extensions
     readonly attribute Window contentWindow;
 
     [CheckSecurity=Node, RaisesException] SVGDocument getSVGDocument();
 };