Add toRenderSVGResourceMasker() fuction, and use it.

Source/core/rendering/svg/SVGRenderTreeAsText.cpp

 /*
  * Copyright (C) 2004, 2005, 2007, 2009 Apple Inc. All rights reserved.
  *           (C) 2005 Rob Buis <buis@kde.org>
  *           (C) 2006 Alexander Kellett <lypanov@kde.org>
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
@@ skipping 469 matching lines @@
     writeStandardPrefix(ts, object, indent);
 
     Element* element = toElement(object.node());
     const AtomicString& id = element->getIdAttribute();
     writeNameAndQuotedValue(ts, "id", id);
 
     RenderSVGResourceContainer* resource = const_cast<RenderObject&>(object).toRenderSVGResourceContainer();
     ASSERT(resource);
 
     if (resource->resourceType() == MaskerResourceType) {
-        RenderSVGResourceMasker* masker = static_cast<RenderSVGResourceMasker*>(resource);
+        RenderSVGResourceMasker* masker = toRenderSVGResourceMasker(resource);
         writeNameValuePair(ts, "maskUnits", masker->maskUnits());
         writeNameValuePair(ts, "maskContentUnits", masker->maskContentUnits());
         ts << "\n";
     } else if (resource->resourceType() == FilterResourceType) {
         RenderSVGResourceFilter* filter = static_cast<RenderSVGResourceFilter*>(resource);
         writeNameValuePair(ts, "filterUnits", filter->filterUnits());
         writeNameValuePair(ts, "primitiveUnits", filter->primitiveUnits());
         ts << "\n";
         // Creating a placeholder filter which is passed to the builder.
         FloatRect dummyRect;
@@ skipping 159 matching lines @@
             ts << " ";
             writeNameAndQuotedValue(ts, "filter", svgStyle->filterResource());
             ts << " ";
             writeStandardPrefix(ts, *filter, 0);
             ts << " " << filter->resourceBoundingBox(&renderer) << "\n";
         }
     }
 }
 
 } // namespace WebCore