Reviewed by David Hyatt.

        Add toRenderImage methods for casting RenderObjects to RenderImages.  The methods will assert if the object
        is not a RenderImage.  Also add a toRenderImage method that takes a RenderImage but returns void and that
        is unimplemented.  This method will catch anyone trying to do a cast when the object is already a RenderImage.

        * html/HTMLAnchorElement.cpp:
        (WebCore::HTMLAnchorElement::defaultEventHandler):
        * html/HTMLEmbedElement.cpp:
        (WebCore::HTMLEmbedElement::attach):
        * html/HTMLImageElement.cpp:
        (WebCore::HTMLImageElement::parseMappedAttribute):
        (WebCore::HTMLImageElement::attach):
        * html/HTMLInputElement.cpp:
        (WebCore::HTMLInputElement::parseMappedAttribute):
        (WebCore::HTMLInputElement::attach):
        * html/HTMLObjectElement.cpp:
        (WebCore::HTMLObjectElement::attach):
        * html/HTMLVideoElement.cpp:
        (WebCore::HTMLVideoElement::attach):
        * loader/ImageLoader.cpp:
        (WebCore::ImageLoader::setImage):
        (WebCore::ImageLoader::updateFromElement):
        (WebCore::ImageLoader::notifyFinished):
        * page/AccessibilityRenderObject.cpp:
        (WebCore::AccessibilityRenderObject::accessibilityIsIgnored):
        (WebCore::AccessibilityRenderObject::addChildren):
        * page/DragController.cpp:
        (WebCore::getCachedImage):
        (WebCore::getImage):
        * platform/mac/PasteboardMac.mm:
        (WebCore::Pasteboard::writeImage):
        * rendering/RenderImage.h:
        (WebCore::toRenderImage):
        * wml/WMLImageElement.cpp:
        (WebCore::WMLImageElement::parseMappedAttribute):
        (WebCore::WMLImageElement::attach):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@40638 268f45cc-cd09-0410-ab3c-d52691b4dbfc