Reviewed by Maciej Stachowiak.

        REGRESSION (WK2): Animated GIF stops when navigating forward, back
        https://bugs.webkit.org/show_bug.cgi?id=59042

        * fast/images/animated-gif-restored-from-bfcache-expected.txt: Added.
        * fast/images/animated-gif-restored-from-bfcache.html: Added.
        * fast/images/resources/animated-10color.gif: Added.
        * platform/mac-wk2/Skipped: Sadly, this test for a WebKit2-specific fix
        has to be skipped for now on WebKit2 since it doesn't implement
        layoutTestController.overridePreference().
2011-04-20  Andy Estes  <aestes@apple.com>

        Reviewed by Maciej Stachowiak.

        REGRESSION (WK2): Animated GIF stops when navigating forward, back
        https://bugs.webkit.org/show_bug.cgi?id=59042

        When loading the page from the b/f cache,
        document()->view()->isOffscreen() returns true in
        RenderObject::willRenderImage(), so BitmapImage::startAnimation()
        returns without actually kicking off the animation.

        In WebKit1, the ScrollView is a platform widget, so
        ScrollView::isOffscreen() calls [NSWindow isVisible]. In WebKit2, the
        ScrollView isn't a platform widget so it asks the WebCore Widget
        whether or not it is visible. It always returns false since
        setParentVisible(false) was called on the old ScrollView before
        navigating to a new page, but setParentVisible(true) is never called
        when restoring it from the back/forward cache. This is probably a
        long-standing bug.

        Fix this by calling setParentVisible(true) when a cached main frame is
        being restored.

        Test: fast/images/animated-gif-restored-from-bfcache.html

        * history/CachedFrame.cpp:
        (WebCore::CachedFrameBase::restore): If the cached frame is the main
        frame, call setParentVisible(true) on the frame's view.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@84443 268f45cc-cd09-0410-ab3c-d52691b4dbfc