Reviewed by David Hyatt.

        [Qt] REGRESSION:(r50665) QWebFrame::setScrollBarPolicy(Qt::Vertical,Qt::ScrollBarAlwaysOff) has no effect.
        https://bugs.webkit.org/show_bug.cgi?id=29431

        Test: fast/overflow/scrollbar-restored-and-then-locked.html

        WebCore:

        Patch introduces a lock scrollbars concept to ScrollView, as in WebDynamicScrollBarsView.mm/h
        on WebKit/mac. It is needed because in QtWebKit, we have Api for setting both vertical and
        horizontal scrollbars on/off/auto. When it is set to off, for example, it should remain
        as such, unless unset.

        For the locking concept, optional 'lock' parameters were added to setScrollbarModes,
        setHorizontalScrollbarMode and setVerticalScrollbarMode methods of ScrollView. As these
        are all optional, any previous code calling them do not need modification.

        Two optional parameters were also added to Frame's createView method, for horizontal and vertical
        lock state persistence cross page loads.

        * WebCore.base.exp:
        * page/Frame.cpp:
        (WebCore::Frame::createView):
        * platform/ScrollView.cpp:
        (WebCore::ScrollView::ScrollView):
        (WebCore::ScrollView::setScrollbarModes):
        (WebCore::ScrollView::setHorizontalScrollbarMode):
        (WebCore::ScrollView::setVerticalScrollbarMode):
        * platform/ScrollView.h:
        (WebCore::ScrollView::setHorizontalScrollbarLock):
        (WebCore::ScrollView::isHorizontalScrollbarLocked):
        (WebCore::ScrollView::setVerticalScrollbarLock):
        (WebCore::ScrollView::isVerticalScrollbarLocked):
        (WebCore::ScrollView::setScrollingModesLocked):

        WebKit/qt:

        Make use of the new lock parameter of set{Vertical,Horizontal}ScrollbarMode.

        Always added a qt auto test for set scrollbar policy feature.

        * Api/qwebframe.cpp:
        (QWebFrame::setScrollBarPolicy):
        * tests/qwebframe/tst_qwebframe.cpp:
        * WebCoreSupport/FrameLoaderClientQt.cpp:
        (FrameLoaderClientQt::transitionToCommittedForNewPage):

        WebKitTools:

        Make possible to DRT to set scrollbar policies (on, off or auto).

        * DumpRenderTree/qt/LayoutTestControllerQt.cpp:
        (LayoutTestController::setScrollbarPolicy):
        * DumpRenderTree/qt/LayoutTestControllerQt.h:
        * QtLauncher/main.cpp:
        (LauncherWindow::toggleScrollbars):
        (LauncherWindow::createChrome):

        LayoutTests:

        * fast/overflow/scrollbar-restored-and-then-locked-expected.txt: Added.
        * fast/overflow/scrollbar-restored-and-then-locked.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@57277 268f45cc-cd09-0410-ab3c-d52691b4dbfc