Move the CSS Device Adaptation @viewport rule support behind a runtime flag

Source/core/dom/Document.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
@@ skipping 1021 matching lines @@
     void didRemoveEventTargetNode(Node*);
 
     const TouchEventTargetSet* touchEventTargets() const { return m_touchEventTargets.get(); }
 
     bool isInDocumentWrite() { return m_writeRecursionDepth > 0; }
 
     void suspendScheduledTasks(ActiveDOMObject::ReasonForSuspension);
     void resumeScheduledTasks();
 
     IntSize viewportSize() const;
-
-#if ENABLE(CSS_DEVICE_ADAPTATION)
     IntSize initialViewportSize() const;
-#endif
 
     Prerenderer* prerenderer() { return m_prerenderer.get(); }
 
     TextAutosizer* textAutosizer() { return m_textAutosizer.get(); }
 
     PassRefPtr<Element> createElement(const AtomicString& localName, const AtomicString& typeExtension, ExceptionCode&);
     PassRefPtr<Element> createElementNS(const AtomicString& namespaceURI, const String& qualifiedName, const AtomicString& typeExtension, ExceptionCode&);
     PassRefPtr<CustomElementConstructor> registerElement(WebCore::ScriptState*, const AtomicString& name, ExceptionCode&);
     PassRefPtr<CustomElementConstructor> registerElement(WebCore::ScriptState*, const AtomicString& name, const Dictionary& options, ExceptionCode&);
     CustomElementRegistry* registry() const { return m_registry.get(); }
@@ skipping 433 matching lines @@
 inline bool Node::isDocumentNode() const
 {
     return this == documentInternal();
 }
 
 Node* eventTargetNodeForDocument(Document*);
 
 } // namespace WebCore
 
 #endif // Document_h