Reviewed by Dan Bernstein

        https://bugs.webkit.org/show_bug.cgi?id=22122

        Use a stack-based object to simplify the pushLayoutState/popLayoutState
        code. LayoutStateMaintainer either pushes in the constructor, or allows
        an explicit push() later. Both cases require an explicit pop().

        * rendering/RenderBlock.cpp:
        (WebCore::RenderBlock::layoutBlock):
        (WebCore::RenderBlock::layoutOnlyPositionedObjects):
        * rendering/RenderContainer.cpp:
        (WebCore::RenderContainer::layout):
        * rendering/RenderFlexibleBox.cpp:
        (WebCore::RenderFlexibleBox::layoutBlock):
        * rendering/RenderTable.cpp:
        (WebCore::RenderTable::layout):
        * rendering/RenderTableRow.cpp:
        (WebCore::RenderTableRow::layout):
        * rendering/RenderTableSection.cpp:
        (WebCore::RenderTableSection::setCellWidths):
        (WebCore::RenderTableSection::calcRowHeight):
        (WebCore::RenderTableSection::layoutRows):
        * rendering/RenderView.h:
        (WebCore::LayoutStateMaintainer::LayoutStateMaintainer):
        (WebCore::LayoutStateMaintainer::~LayoutStateMaintainer):
        (WebCore::LayoutStateMaintainer::pop):
        (WebCore::LayoutStateMaintainer::push):
        (WebCore::LayoutStateMaintainer::didPush):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@38227 268f45cc-cd09-0410-ab3c-d52691b4dbfc