2009-07-30  Darin Adler  <darin@apple.com>

        Reviewed by David Levin.

        Use checked casts for render tree
        https://bugs.webkit.org/show_bug.cgi?id=23522

        Next step: Add casts for all the RenderTable classes and use them everywhere.

        Also added a few uses in places that were still using static_cast.
        Also made some virtual member functions private.
        Also changed RenderTable::m_tableLayout to use OwnPtr.

        * accessibility/AccessibilityTable.cpp:
        (WebCore::AccessibilityTable::isTableExposableThroughAccessibility):
        (WebCore::AccessibilityTable::addChildren):
        (WebCore::AccessibilityTable::cellForColumnAndRow):
        * accessibility/AccessibilityTableCell.cpp:
        (WebCore::AccessibilityTableCell::parentTable):
        (WebCore::AccessibilityTableCell::rowIndexRange):
        (WebCore::AccessibilityTableCell::columnIndexRange):
        (WebCore::AccessibilityTableCell::titleUIElement):
        * accessibility/Access...