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

Source/core/dom/Document.cpp

 /*
  * 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, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 5251 matching lines @@
     return loader;
 }
 
 IntSize Document::viewportSize() const
 {
     if (!view())
         return IntSize();
     return view()->visibleContentRect(ScrollableArea::IncludeScrollbars).size();
 }
 
-#if ENABLE(CSS_DEVICE_ADAPTATION)
 IntSize Document::initialViewportSize() const
 {
     if (!view())
         return IntSize();
-    return view()->initialViewportSize();
+    return view()->unscaledVisibleContentSize(ScrollableArea::IncludeScrollbars);
 }
-#endif
 
 Node* eventTargetNodeForDocument(Document* doc)
 {
     if (!doc)
         return 0;
     Node* node = doc->focusedNode();
     if (!node && doc->isPluginDocument()) {
         PluginDocument* pluginDocument = toPluginDocument(doc);
         node =  pluginDocument->pluginNode();
     }
@@ skipping 303 matching lines @@
         return;
 
     Vector<RefPtr<Element> > associatedFormControls;
     copyToVector(m_associatedFormControls, associatedFormControls);
 
     frame()->page()->chrome().client()->didAssociateFormControls(associatedFormControls);
     m_associatedFormControls.clear();
 }
 
 } // namespace WebCore