Remove the ENABLE_IFRAME_SEAMLESS compile-time flag.

Source/WebCore/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 41 matching lines @@
     display: none
 }
 
 /* generic block-level elements */
 
 body {
     display: block;
     margin: 8px
 }
 
-#if defined(ENABLE_IFRAME_SEAMLESS) && ENABLE_IFRAME_SEAMLESS
 body:-webkit-seamless-document {
     margin: 0px;
 }
-#endif
 
 p {
     display: block;
     -webkit-margin-before: 1__qem;
     -webkit-margin-after: 1__qem;
     -webkit-margin-start: 0;
     -webkit-margin-end: 0;
 }
 
 div {
@@ skipping 1233 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. */