Introduce toSVGPatternElement(), use it

Source/core/rendering/svg/RenderSVGResourcePattern.cpp

 /*
  * Copyright (C) 2006 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) Research In Motion Limited 2010. 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 40 matching lines @@
     m_patternMap.remove(client);
     markClientForInvalidation(client, markForInvalidation ? RepaintInvalidation : ParentOnlyInvalidation);
 }
 
 PatternData* RenderSVGResourcePattern::buildPattern(RenderObject* object, unsigned short resourceMode)
 {
     PatternData* currentData = m_patternMap.get(object);
     if (currentData && currentData->pattern)
         return currentData;
 
-    SVGPatternElement* patternElement = static_cast<SVGPatternElement*>(node());
+    SVGPatternElement* patternElement = toSVGPatternElement(node());
     if (!patternElement)
         return 0;
 
     if (m_shouldCollectPatternAttributes) {
         patternElement->synchronizeAnimatedSVGAttribute(anyQName());
 
         m_attributes = PatternAttributes();
         patternElement->collectPatternAttributes(m_attributes);
         m_shouldCollectPatternAttributes = false;
     }
@@ skipping 193 matching lines @@
             continue;
         if (node->renderer()->needsLayout())
             return nullptr;
         SVGRenderingContext::renderSubtreeToImageBuffer(tileImage.get(), node->renderer(), contentTransformation);
     }
 
     return tileImage.release();
 }
 
 }