Add Frame::cleanupScriptObjectsForPlugin which will invalidate the root object
        for a given plug-in.

        * WebCore.exp:
        * page/Frame.cpp:
        (WebCore::Frame::cleanupScriptObjectsForPlugin):
        * page/Frame.h:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@23536 268f45cc-cd09-0410-ab3c-d52691b4dbfc