another Web Inspector window would not show any scripts.
        Also only attach the debugger to only the required Pages.

        https://bugs.webkit.org/show_bug.cgi?id=21708

        Reviewed by Darin Adler.

        * inspector/JavaScriptDebugServer.cpp:
        (WebCore::JavaScriptDebugServer::addListener): Add an assert and
        remove the call to willAddFirstListener(). Add a call to
        didAddListener().
        (WebCore::JavaScriptDebugServer::removeListener): Add an assert
        and call to didRemoveListener().
        (WebCore::JavaScriptDebugServer::pageCreated): Attach the debugger
        if there is a listener interested in the new Page.
        (WebCore::JavaScriptDebugServer::hasListenersInterestedInPage):
        Use hasGlobalListeners() instead of isEmpty().
        (WebCore::JavaScriptDebugServer::sourceParsed): Ditto.
        (WebCore::JavaScriptDebugServer::didAddListener): Added. Attach the
        debugger to the page if non-null, or all pages if page is null.
        (WebCore::JavaScriptDebugServer::didRemoveListener): Added. Detach
        the debugger only if there are no interested listeners.
        (WebCore::JavaScriptDebugServer::didRemoveLastListener): Remove the
        call to Page::setDebuggerForAllPages().
        * inspector/JavaScriptDebugServer.h:
        (WebCore::JavaScriptDebugServer::hasGlobalListeners): Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@37656 268f45cc-cd09-0410-ab3c-d52691b4dbfc