Reviewed by Kenneth Rohde Christiansen.

        [Qt] Spatial Navigation: adding a test for when scrollbars are turned off via WebKit API
        https://bugs.webkit.org/show_bug.cgi?id=51396

        Add a layout test to ensure that page is scrollable when spatial
        navgation is enabled even when scrollbars were disabled via WebKit
        API (e.g. QWebFrame::setScrollBarPolicy).

        Test is Qt-only for now since Qt's DRT is the only one that supports
        LayoutTestController::setScrollbarPolicy.

        In real world QtWebKit apps, scrollbars are disabled usually prior to
        any page load. To emulate that on a layout test, it was added two html
        files: one that set scrollbars off and queues the load of the real
        test, and other that does the real testing.

        * platform/qt/fast/spatial-navigation/resources/ensure-scrolls-with-scrollbars-disabled-by-webkit.html: Added.
        * platform/qt/fast/spatial-navigation/snav-ensure-scrolls-with-scrollbars-disabled-by-webkit-expected.txt: Added.
        * platform/qt/fast/spatial-navigation/snav-ensure-scrolls-with-scrollbars-disabled-by-webkit.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@75321 268f45cc-cd09-0410-ab3c-d52691b4dbfc