Fix for <rdar://problem/4610314> Support the CSS3 content property 
        for images

        This patch provides initial support for the CSS3 content property. 
        It lacks support for any content other than images, and only allows 
        content for elements that seemed safe for now.

        * css/cssstyleselector.cpp:
        (WebCore::CSSStyleSelector::applyProperty): Remove restrictions for 
        just :before and :after
        * html/HTMLBRElement.cpp:
        (WebCore::HTMLBRElement::createRenderer):
        * html/HTMLFrameSetElement.cpp:
        (WebCore::HTMLFrameSetElement::createRenderer):
        * html/HTMLImageElement.cpp:
        (WebCore::HTMLImageElement::createRenderer):
        * html/HTMLLegendElement.cpp:
        (WebCore::HTMLLegendElement::createRenderer):
        * rendering/RenderImage.cpp:
        (WebCore::RenderImage::RenderImage):
        (WebCore::RenderImage::setCachedImage): Don't allow the image to be 
        set this way if it was already set with the content property.
        * rendering/RenderImage.h:
        (WebCore::RenderImage::setIsAnonymousImage): Anonymous images are 
        those set through the content property.
        (WebCore::RenderImage::isAnonymousImage):
        * rendering/RenderObject.cpp:
        (WebCore::RenderObject::createObject): If there is content 
        specified, create a RenderImage with the content and initialize the 
        cached image to whatever was specified in the CSS.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@15299 268f45cc-cd09-0410-ab3c-d52691b4dbfc