Reviewed by Maciej.

        track onbeforeunlaod event counts. Pretty much identical to unload event tracking.
        Also rename methods from onunload tracking to be more clear.

        increment/decrement event counts when onunload and onbeforeunload events are added/removed
        * dom/Document.cpp:
        (WebCore::Document::removeHTMLWindowEventListener):
        (WebCore::Document::addWindowEventListener):
        (WebCore::Document::removeWindowEventListener):
        (WebCore::Document::addPendingFrameUnloadEventCount):
        (WebCore::Document::removePendingFrameUnloadEventCount):
        (WebCore::Document::addPendingFrameBeforeUnloadEventCount):
        (WebCore::Document::removePendingFrameBeforeUnloadEventCount):
        * dom/Document.h:
        
        clear onunload count after unload events are dispatched
        * loader/FrameLoader.cpp:
        (WebCore::FrameLoader::stopLoading):

        track onunload and onbeforeunload event counts for each frame
        * page/EventHandler.cpp:
        (WebCore::EventHandler::EventHandler):
        (WebCore::EventHandler::addPendingFrameUnloadEventCount):
        (WebCore::EventHandler::removePendingFrameUnloadEventCount):
        (WebCore::EventHandler::clearPendingFrameUnloadEventCount):
        (WebCore::EventHandler::pendingFrameBeforeUnloadEventCount):
        (WebCore::EventHandler::addPendingFrameBeforeUnloadEventCount):
        (WebCore::EventHandler::removePendingFrameBeforeUnloadEventCount):
        (WebCore::EventHandler::clearPendingFrameBeforeUnloadEventCount):
        * page/EventHandler.h:
        
        clear unbeforeunload count after unbeforeunload events are detached
        * page/Frame.cpp:
        (WebCore::Frame::shouldClose):

        track total event count at page level
        * page/Page.cpp:
        (WebCore::Page::Page):
        (WebCore::Page::changePendingUnloadEventCount):
        (WebCore::Page::pendingBeforeUnloadEventCount):
        (WebCore::Page::changePendingBeforeUnloadEventCount):
        * page/Page.h:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@33538 268f45cc-cd09-0410-ab3c-d52691b4dbfc