Reviewed by Oliver Hunt.

        Added some write barrier action, compiled out by default
        https://bugs.webkit.org/show_bug.cgi?id=62844

        * JavaScriptCore.exp: Build!

        * JavaScriptCore.xcodeproj/project.pbxproj: Fixed an incremental build
        issue with Heap.cpp.

        * heap/Heap.cpp:
        (JSC::Heap::writeBarrierSlowCase):
        * heap/Heap.h:
        (JSC::Heap::writeBarrier):
        * heap/MarkedBlock.h:
        (JSC::MarkedBlock::isAtomAligned):
        (JSC::MarkedBlock::blockFor):
        (JSC::MarkedBlock::atomNumber):
        (JSC::MarkedBlock::ownerSetNumber):
        (JSC::MarkedBlock::addOldSpaceOwner):
        (JSC::MarkedBlock::OwnerSet::OwnerSet):
        (JSC::MarkedBlock::OwnerSet::add):
        (JSC::MarkedBlock::OwnerSet::clear):
        (JSC::MarkedBlock::OwnerSet::size):
        (JSC::MarkedBlock::OwnerSet::didOverflow):
        (JSC::MarkedBlock::OwnerSet::owners): Added a basic write barrier that
        tracks owners for regions within blocks. Currently unused.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@89156 268f45cc-cd09-0410-ab3c-d52691b4dbfc