Remove viewportConstrained plumbing.

sky/engine/core/rendering/compositing/CompositingTriggers.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple, Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  * Copyright (C) 2012 Samsung Electronics. 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.
  *
  * 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.
  */
 
 #ifndef CompositingTriggers_h
 #define CompositingTriggers_h
 
 namespace blink {
 
 enum CompositingTrigger {
     ScrollableInnerFrameTrigger = 1 << 1,
     OverflowScrollTrigger = 1 << 2,
-    ViewportConstrainedPositionedTrigger = 1 << 3,
     AllCompositingTriggers = 0xFFFFFFFF,
 };
 
 typedef unsigned CompositingTriggerFlags;
 
 }
 
 #endif