Reviewed by Oliver Hunt.

        Made MarkedBlock variable-sized
        https://bugs.webkit.org/show_bug.cgi?id=54692
        
        SunSpider reports no change.
        
        Each MarkedBlock is now composed of a set of fixed-sized atoms, with one
        mark bit per atom. A given cell may be composed of one or more atoms.
        
        * runtime/Heap.cpp:
        (JSC::Heap::allocate): Made fixed-sizedness a property of MarkedSpace,
        bubbling it up from MarkedBlock, since MarkedBlock now supports variable-
        sizedness.

        * runtime/JSCell.h:
        (JSC::JSCell::MarkedBlock::allocate): Removed use of CELLS_PER_BLOCK and
        (implicit) one constants -- these quantities are not constant anymore.
        Updated for switch from cell to atom.

        * runtime/MarkedBlock.cpp:
        (JSC::MarkedBlock::create):
        (JSC::MarkedBlock::destroy):
        (JSC::MarkedBlock::MarkedBlock):
        (JSC::MarkedBlock::sweep):
        * runtime/MarkedBlock.h:
        (JSC::MarkedBlock::firstAtom):
        (JSC::MarkedBlock::atoms):
        (JSC::MarkedBlock::isAtomAligned):
        (JSC::MarkedBlock::blockFor):
        (JSC::MarkedBlock::isEmpty):
        (JSC::MarkedBlock::clearMarks):
        (JSC::MarkedBlock::size):
        (JSC::MarkedBlock::capacity):
        (JSC::MarkedBlock::atomNumber):
        (JSC::MarkedBlock::isMarked):
        (JSC::MarkedBlock::testAndSetMarked):
        (JSC::MarkedBlock::setMarked):
        (JSC::MarkedBlock::forEach): Same as above. Also removed use of CELL_SIZE
        and BLOCK_SIZE, and switched away from calling arbitrary pointers cells.

        * runtime/MarkedSpace.cpp:
        (JSC::MarkedSpace::MarkedSpace):
        (JSC::MarkedSpace::allocateBlock):
        (JSC::MarkedSpace::allocate):
        (JSC::MarkedSpace::reset):
        * runtime/MarkedSpace.h:
        (JSC::CollectorHeap::CollectorHeap):
        (JSC::MarkedSpace::contains): Updated for renames. Made fixed-sizedness
        a property of MarkedSpace.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@78924 268f45cc-cd09-0410-ab3c-d52691b4dbfc