Don't always fully repaint on viewport resize

Source/core/rendering/style/FillLayer.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *
  * 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
@@ skipping 149 matching lines @@
         return m_next ? m_next->hasImage() : false;
     }
 
     bool hasFixedImage() const
     {
         if (m_image && m_attachment == FixedBackgroundAttachment)
             return true;
         return m_next ? m_next->hasFixedImage() : false;
     }
 
+    bool needsFullRepaintOnContainerWidthChange() const;
+    bool needsFullRepaintOnContainerHeightChange() const;
+
     bool hasOpaqueImage(const RenderObject*) const;
     bool hasRepeatXY() const;
     bool clipOccludesNextLayers(bool firstLayer) const;
 
     EFillLayerType type() const { return static_cast<EFillLayerType>(m_type); }
 
     void fillUnsetProperties();
     void cullEmptyLayers();
 
     static EFillAttachment initialFillAttachment(EFillLayerType) { return ScrollBackgroundAttachment; }
@@ skipping 54 matching lines @@
     unsigned m_maskSourceTypeSet : 1;
 
     unsigned m_type : 1; // EFillLayerType
 
     mutable unsigned m_clipMax : 2; // EFillBox, maximum m_clip value from this to bottom layer
 };
 
 } // namespace WebCore
 
 #endif // FillLayer_h