Remove the ENABLE_IFRAME_SEAMLESS compile-time flag.

Source/WebCore/css/CSSSelector.h

 /*
  * Copyright (C) 1999-2003 Lars Knoll (knoll@kde.org)
  *               1999 Waldo Bastian (bastian@kde.org)
  * Copyright (C) 2004, 2006, 2007, 2008, 2009, 2010, 2013 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 146 matching lines @@
             PseudoAnimatingFullScreenTransition,
             PseudoInRange,
             PseudoOutOfRange,
             PseudoUserAgentCustomElement,
             PseudoWebKitCustomElement,
 #if ENABLE(VIDEO_TRACK)
             PseudoCue,
             PseudoFutureCue,
             PseudoPastCue,
 #endif
-#if ENABLE(IFRAME_SEAMLESS)
             PseudoSeamlessDocument,
-#endif
 #if ENABLE(SHADOW_DOM)
             PseudoDistributed
 #endif
         };
 
         enum MarginBoxType {
             TopLeftCornerMarginBox,
             TopLeftMarginBox,
             TopCenterMarginBox,
             TopRightMarginBox,
@@ skipping 271 matching lines @@
     ASSERT(m_match != Tag);
     // AtomicString is really just an AtomicStringImpl* so the cast below is safe.
     // FIXME: Perhaps call sites could be changed to accept AtomicStringImpl?
     return *reinterpret_cast<const AtomicString*>(m_hasRareData ? &m_data.m_rareData->m_value : &m_data.m_value);
 }
 
 
 } // namespace WebCore
 
 #endif // CSSSelector_h