Reviewed by Darin.

        Most of the implementation for https://bugs.webkit.org/show_bug.cgi?id=17998
        When a resource is cached locally, WebKit should follow RFC 2616 "Specific end-to-end revalidation" instead of "Unspecified end-to-end revalidation"

        Implement HTTP 1.1 "Specific end-to-end revalidation" for WebCore memory cache. This patch does
        not yet enable it for the biggest use case, reloading. However it is good for general browsing as
        well. Doing this in WebCore level as opposed to relying on disk cache has big benefit that
        we avoid re-decoding resources, especially images. 
        
        To be exact the enabled case is not actually the "Specific end-to-end revalidation" since it does not include
        CacheControl: max-age=0 header. That would be added in reload case.
        
        The approach for revalidation is to kick the original resource out from the memory cache
        and create a new CachedResource that represents the revalidation request. In case
        we get 304 back for the request we put the original resource back to the cache, update 
        its expiration date and switch the clients registered to revalidation resource to be
        clients of the original resource.
        
        All heap allocated CachedImage pointers now use CachedResourceHandle<CachedImage> (and so on) instead.
        This allows updating the handles to point to the original resource when the revalidation succeeds. It
        also acts as refcounting smart pointer.

        * WebCore.pro:
        * WebCore.vcproj/WebCore.vcproj:
        * WebCore.xcodeproj/project.pbxproj:
        * css/CSSFontFaceSource.h:
        * css/CSSImportRule.h:
        * dom/Clipboard.h:
        (WebCore::Clipboard::dragImage):
        * dom/ProcessingInstruction.h:
        * dom/ScriptElement.h:
        * dom/XMLTokenizer.cpp:
        (WebCore::XMLTokenizer::isWaitingForScripts):
        * dom/XMLTokenizer.h:
        * html/HTMLImageLoader.cpp:
        (WebCore::HTMLImageLoader::setImage):
        (WebCore::HTMLImageLoader::updateFromElement):
        (WebCore::HTMLImageLoader::notifyFinished):
        * html/HTMLImageLoader.h:
        (WebCore::HTMLImageLoader::image):
        * html/HTMLLinkElement.h:
        * html/HTMLTokenizer.cpp:
        (WebCore::HTMLTokenizer::reset):
        (WebCore::HTMLTokenizer::scriptHandler):
        (WebCore::HTMLTokenizer::notifyFinished):
        * html/HTMLTokenizer.h:
        * loader/Cache.cpp:
        (WebCore::Cache::revalidateResource):
        (WebCore::Cache::revalidationSucceeded):
        (WebCore::Cache::revalidationFailed):
        * loader/Cache.h:
        * loader/CachedResource.cpp:
        (WebCore::CachedResource::CachedResource):
        (WebCore::CachedResource::~CachedResource):
        (WebCore::CachedResource::isExpired):
        (WebCore::CachedResource::setResponse):
        (WebCore::CachedResource::deleteIfPossible):
        (WebCore::CachedResource::setResourceToRevalidate):
        (WebCore::CachedResource::clearResourceToRevalidate):
        (WebCore::CachedResource::switchClientsToRevalidatedResource):
        (WebCore::CachedResource::canUseCacheValidator):
        (WebCore::CachedResource::mustRevalidate):
        * loader/CachedResource.h:
        (WebCore::CachedResource::canDelete):
        (WebCore::CachedResource::registerHandle):
        (WebCore::CachedResource::unregisterHandle):
        (WebCore::CachedResource::isCacheValidator):
        (WebCore::CachedResource::resourceToRevalidate):
        (WebCore::CachedResource::setExpirationDate):
        * loader/CachedResourceHandle.cpp: Added.
        (WebCore::CachedResourceHandleBase::setResource):
        * loader/CachedResourceHandle.h: Added.
        (WebCore::CachedResourceHandleBase::~CachedResourceHandleBase):
        (WebCore::CachedResourceHandleBase::get):
        (WebCore::CachedResourceHandleBase::operator!):
        (WebCore::CachedResourceHandleBase::operator UnspecifiedBoolType):
        (WebCore::CachedResourceHandleBase::CachedResourceHandleBase):
        (WebCore::CachedResourceHandleBase::operator=):
        (WebCore::CachedResourceHandle::CachedResourceHandle):
        (WebCore::CachedResourceHandle::get):
        (WebCore::CachedResourceHandle::operator->):
        (WebCore::CachedResourceHandle::operator=):
        (WebCore::CachedResourceHandle::operator==):
        (WebCore::CachedResourceHandle::operator!=):
        (WebCore::operator==):
        (WebCore::operator!=):
        * loader/DocLoader.cpp:
        (WebCore::DocLoader::checkForReload):
        * loader/UserStyleSheetLoader.h:
        * loader/loader.cpp:
        (WebCore::Loader::Host::servePendingRequests):
        (WebCore::Loader::Host::didFinishLoading):
        (WebCore::Loader::Host::didFail):
        (WebCore::Loader::Host::didReceiveResponse):
        (WebCore::Loader::Host::didReceiveData):
        * page/EventHandler.cpp:
        (WebCore::EventHandler::selectCursor):
        * rendering/RenderImage.cpp:
        (WebCore::RenderImage::setCachedImage):
        (WebCore::RenderImage::imageChanged):
        * rendering/RenderImage.h:
        (WebCore::RenderImage::cachedImage):
        (WebCore::RenderImage::imagePtr):
        * rendering/style/RenderStyle.h:
        * rendering/style/StyleCachedImage.h:
        (WebCore::StyleCachedImage::data):
        (WebCore::StyleCachedImage::cachedImage):
        * svg/SVGFEImageElement.h:
        * svg/graphics/filters/SVGFEImage.h:
        * xml/XSLImportRule.h:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@36109 268f45cc-cd09-0410-ab3c-d52691b4dbfc