Reviewed by Dave Hyatt.

        - fix http://bugs.webkit.org/show_bug.cgi?id=15015
          <rdar://problem/5420308> Most of www.aol.com redraws unnecessarily when headline/photo section changes

        Test: fast/repaint/overflow-clip-subtree-layout.html

        This patch does not address the bigger issue of doing a full relayout
        of inline flows containing floats, but it addresses the problem on
        aol.com, where the changes that trigger layout are confined to an
        overflow area inside the float.

        * page/FrameView.cpp:
        (WebCore::FrameView::scheduleRelayoutOfSubtree): If the new and old
        layout roots are different but one descends from the other, make (or
        keep) the ancestor as the layout root.
        * rendering/RenderObject.cpp:
        (WebCore::objectIsRelayoutBoundary): Made boxes with overflow
        clipping and non-auto width and height relayout boundaries.

LayoutTests:

        Reviewed by Dave Hyatt.

        - repaint test for http://bugs.webkit.org/show_bug.cgi?id=15015
          <rdar://problem/5420308> Most of www.aol.com redraws unnecessarily when headline/photo section changes

        * fast/repaint/overflow-clip-subtree-layout.html: Added.
        * platform/mac/fast/repaint/overflow-clip-subtree-layout-expected.checksum: Added.
        * platform/mac/fast/repaint/overflow-clip-subtree-layout-expected.png: Added.
        * platform/mac/fast/repaint/overflow-clip-subtree-layout-expected.txt: Added.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@27351 268f45cc-cd09-0410-ab3c-d52691b4dbfc