Reviewed by Darin Adler.

        Refactored MarkedSpace to operate in terms of size classes
        https://bugs.webkit.org/show_bug.cgi?id=55106
        
        SunSpider reports no change.

        * runtime/JSCell.h:
        (JSC::JSCell::MarkedSpace::sizeClassFor):
        (JSC::JSCell::MarkedSpace::allocate): Delegate allocation based on size
        class. Since these functions are inline, the compiler can constant fold
        them.

        * runtime/MarkedBlock.h:
        (JSC::MarkedBlock::cellSize):
        (JSC::MarkedBlock::size): Factored out a cellSize() helper.

        * runtime/MarkedSpace.cpp:
        (JSC::MarkedSpace::allocateBlock):
        (JSC::MarkedSpace::allocateFromSizeClass):
        (JSC::MarkedSpace::shrink):
        (JSC::MarkedSpace::reset):
        * runtime/MarkedSpace.h:
        (JSC::MarkedSpace::SizeClass::SizeClass):
        (JSC::MarkedSpace::SizeClass::reset): Changed to operate in terms of
        abstract SizeClass objects, which are independent linked lists of blocks
        of a certain size class, instead of a single m_heap object.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@79512 268f45cc-cd09-0410-ab3c-d52691b4dbfc