Reviewed by Tony Gentilcore.

        Implement onerror events for <link rel=prefetch>
        https://bugs.webkit.org/show_bug.cgi?id=57182

        * fast/dom/HTMLLinkElement/prefetch-onerror-expected.txt: Added.
        * fast/dom/HTMLLinkElement/prefetch-onerror.html: Added.
        * platform/gtk/Skipped:
        * platform/mac/Skipped:
        * platform/qt/Skipped:
        * platform/win/Skipped:
2011-03-29  Gavin Peters  <gavinp@chromium.org>

        Reviewed by Tony Gentilcore.

        Implement onerror events for <link rel=prefetch>
        https://bugs.webkit.org/show_bug.cgi?id=57182

        These events are equired on link elements, see
        http://dev.w3.org/html5/spec/Overview.html#the-link-element

        After a discussion in WebKit-dev about the direction of prefetch in the loader, and about a path
        to adding the Link header, we decided to look at making onerror, onload and onbeforeload events
        more uniformly supported.  See the thread at
        https://lists.webkit.org/pipermail/webkit-dev/2011-February/016034.html .

        It turned out that part of adding onerror for link prefetch was to make the top CachedResource less
        abstract.  It was pure virtual until prefetch became the first consumer to use an unspecialised
        implementation, and this CL continues that by adding a default checkNotify method to it.  As it
        happens there were already two subclasses using what amounted to the generic checkNotify, so I
        also removed those, buying us some code cleanup with the change.

        Test: fast/dom/HTMLLinkElement/prefetch-onerror.html

        * html/HTMLLinkElement.cpp:
        (WebCore::HTMLLinkElement::parseMappedAttribute):
        (WebCore::HTMLLinkElement::onloadTimerFired):
        (WebCore::HTMLLinkElement::notifyFinished):
        * loader/cache/CachedImage.cpp:
        * loader/cache/CachedImage.h:
        * loader/cache/CachedResource.cpp:
        (WebCore::CachedResource::checkNotify):
        (WebCore::CachedResource::data):
        (WebCore::CachedResource::error):
        * loader/cache/CachedResource.h:
        * loader/cache/CachedScript.cpp:
        * loader/cache/CachedScript.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@82217 268f45cc-cd09-0410-ab3c-d52691b4dbfc