Reviewed by Kenneth Rohde Christiansen.

        [Qt] Make possible run DRT with QGraphicsWebView
        https://bugs.webkit.org/show_bug.cgi?id=40016

        Make possible to use a environment variable for switching backend.
        Usage: QT_DRT_WEBVIEW_MODE=graphics WebKitTools/Scripts/run-webkit-tests --qt

        * DumpRenderTree/qt/DumpRenderTreeQt.cpp:
        (WebCore::WebViewGraphicsBased::WebViewGraphicsBased):
        (WebCore::DumpRenderTree::DumpRenderTree):
        * DumpRenderTree/qt/DumpRenderTreeQt.h:
        (WebCore::DumpRenderTree::setGraphicsBased):
        (WebCore::DumpRenderTree::isGraphicsBased):
        (WebCore::WebViewGraphicsBased::graphicsView):
        (WebCore::WebViewGraphicsBased::setPage):
        * Scripts/old-run-webkit-tests:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@60586 268f45cc-cd09-0410-ab3c-d52691b4dbfc