Introduce toHTMLInputElement(Node*), and use it.

Source/core/rendering/RenderImage.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011-2012. All rights reserved.
  *
@@ skipping 508 matching lines @@
         result = tempResult;
     return inside;
 }
 
 void RenderImage::updateAltText()
 {
     if (!node())
         return;
 
     if (node()->hasTagName(inputTag))
-        m_altText = static_cast<HTMLInputElement*>(node())->altText();
+        m_altText = toHTMLInputElement(node())->altText();
     else if (node()->hasTagName(imgTag))
         m_altText = static_cast<HTMLImageElement*>(node())->altText();
 }
 
 void RenderImage::layout()
 {
     StackStats::LayoutCheckPoint layoutCheckPoint;
     RenderReplaced::layout();
 
     // Propagate container size to image resource.
@@ skipping 35 matching lines @@
         return 0;
 
     CachedImage* cachedImage = m_imageResource->cachedImage();
     if (cachedImage && cachedImage->image() && cachedImage->image()->isSVGImage())
         return static_cast<SVGImage*>(cachedImage->image())->embeddedContentBox();
 
     return 0;
 }
 
 } // namespace WebCore