Linux/gdk build fixes - add new files based on qt implementation.

        * page/gdk/DragControllerGdk.cpp: Added.
        (WebCore::DragController::dragOperation):
        * page/gdk/EventHandlerGdk.cpp: Added.
        (WebCore::EventHandler::focusDocumentView):
        (WebCore::EventHandler::passWidgetMouseDownEventToWidget):
        (WebCore::EventHandler::handleDrag):
        (WebCore::EventHandler::eventActivatedView):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@19476 268f45cc-cd09-0410-ab3c-d52691b4dbfc