- fix http://bugs.webkit.org/show_bug.cgi?id=12347
          REGRESSION: list box scrolling broken (fast/forms/listbox-selection.html)

        Covered by existing test: fast/forms/listbox-selection.html

        * rendering/RenderListBox.h: Added override of layout(), made selectionChanged()
        no longer an inline. Added private scrollToRevealSelection(),
        m_scrollToRevealSelectionAfterLayout, and m_inAutoscroll.
        * rendering/RenderListBox.cpp:
        (WebCore::RenderListBox::RenderListBox): Initialize new data members.
        (WebCore::RenderListBox::updateFromElement): Remove scrolling code.
        (WebCore::RenderListBox::selectionChanged): Moved from header. Calls repaint
        and then scrollToRevealSelection, but if we need layout, instead schedules
        scrollToRevealSelection to be done after layout.
        (WebCore::RenderListBox::layout): Added. After calling base class, calls
        scrollToRevealSelection if the m_scrollToRevealSelectionAfterLayout is set.
        (WebCore::RenderListBox::scrollToRevealSelection): Added. Code was originally
        in updateFromElement.
        (WebCore::RenderListBox::autoscroll): Set m_inAutoscroll so that the
        selectionChanged function knows not to scroll. Also removed the repaint()
        here because updateListBoxSelection() takes care of repainting by calling
        selectionChanged().



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@19008 268f45cc-cd09-0410-ab3c-d52691b4dbfc