Move viewport unit resolution to style recalc time

Source/core/css/resolver/MatchedPropertiesCache.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Google 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 36 matching lines @@
 
 class MatchedPropertiesCache {
     WTF_MAKE_NONCOPYABLE(MatchedPropertiesCache);
 public:
     MatchedPropertiesCache();
 
     const CachedMatchedProperties* find(unsigned hash, const StyleResolverState&, const MatchResult&);
     void add(const RenderStyle*, const RenderStyle* parentStyle, unsigned hash, const MatchResult&);
 
     void clear();
+    void clearViewportDependent();
 
     static bool isCacheable(const Element*, const RenderStyle*, const RenderStyle* parentStyle);
 
 private:
     // Every N additions to the matched declaration cache trigger a sweep where entries holding
     // the last reference to a style declaration are garbage collected.
     void sweep(Timer<MatchedPropertiesCache>*);
 
     unsigned m_additionsSinceLastSweep;
 
     typedef HashMap<unsigned, OwnPtr<CachedMatchedProperties> > Cache;
     Cache m_cache;
 
     Timer<MatchedPropertiesCache> m_sweepTimer;
 };
 
 }
 
 #endif