Reviewed by Darin Fisher.
        
        Implement <a ping> (disabled by default).
        https://bugs.webkit.org/show_bug.cgi?id=30458
        
        Tests: http/tests/navigation/ping-cross-origin-from-https.html
               http/tests/navigation/ping-cross-origin.html
               http/tests/navigation/ping-same-origin.html

        * html/HTMLAnchorElement.cpp:
        (WebCore::HTMLAnchorElement::defaultEventHandler):
        (WebCore::HTMLAnchorElement::sendPings):
        * html/HTMLAnchorElement.h:
        * html/HTMLAttributeNames.in:
        * loader/PingLoader.cpp:
        (WebCore::PingLoader::sendPing): Set ping-specific headers.
        (WebCore::PingLoader::PingLoader):
        * loader/PingLoader.h:
        (WebCore::PingLoader::timeout): Ensure pings eventually timeout, since
            the normal cancel mechanism can't stop them.
        * page/Settings.cpp:
        * page/Settings.h: Add hyperlinkAuditingEnabled.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@68166 268f45cc-cd09-0410-ab3c-d52691b4dbfc