Reviewed by Adam Barth.

        Add callbacks to ScriptController to allow notifications on named items additions and removals
        https://bugs.webkit.org/show_bug.cgi?id=39679

        * bindings/js/ScriptController.h: Callbacks with empty implementation added.
        (WebCore::ScriptController::namedItemAdded):
        (WebCore::ScriptController::namedItemRemoved):
        * bindings/v8/ScriptController.cpp: Empty implementation of callbacks.
        (WebCore::ScriptController::namedItemAdded):
        (WebCore::ScriptController::namedItemRemoved):
        * bindings/v8/ScriptController.h: Callbacks added.
        * html/HTMLDocument.cpp: Hooking in callbacks.
        (WebCore::HTMLDocument::addItemToMap):
        (WebCore::HTMLDocument::removeItemFromMap):
        * html/HTMLDocument.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@60291 268f45cc-cd09-0410-ab3c-d52691b4dbfc