Web Animations CSS: Fix crash when transitioning background or mask properties

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 44 matching lines @@
         return !(*this == o);
     }
 
     EFillSizeType type;
     LengthSize size;
 };
 
 class FillLayer {
     WTF_MAKE_FAST_ALLOCATED;
 public:
-    FillLayer(EFillLayerType);
+    FillLayer(EFillLayerType, bool useInitialValues = false);
     ~FillLayer();
 
     StyleImage* image() const { return m_image.get(); }
     Length xPosition() const { return m_xPosition; }
     Length yPosition() const { return m_yPosition; }
     BackgroundEdgeOrigin backgroundXOrigin() const { return static_cast<BackgroundEdgeOrigin>(m_backgroundXOrigin); }
     BackgroundEdgeOrigin backgroundYOrigin() const { return static_cast<BackgroundEdgeOrigin>(m_backgroundYOrigin); }
     EFillAttachment attachment() const { return static_cast<EFillAttachment>(m_attachment); }
     EFillBox clip() const { return static_cast<EFillBox>(m_clip); }
     EFillBox origin() const { return static_cast<EFillBox>(m_origin); }
@@ skipping 158 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