Reviewed by Maciej Stachowiak.

        Cleaned up some conservative marking code.
        https://bugs.webkit.org/show_bug.cgi?id=52946
        
        SunSpider reports no change.

        * interpreter/RegisterFile.h: No need for a special marking function,
        since we already expose a start() and end().

        * runtime/Heap.cpp:
        (JSC::Heap::registerFile):
        (JSC::Heap::markRoots):
        * runtime/Heap.h:
        (JSC::Heap::contains): Migrated markConservatively() to the machine stack
        marker class. Now, Heap just provides a contains() function, which the
        machine stack marker uses for checking whether a pointer points into the heap.

        * runtime/MachineStackMarker.cpp:
        (JSC::MachineStackMarker::markCurrentThreadConservativelyInternal):
        (JSC::MachineStackMarker::markOtherThreadConservatively):
        (JSC::isPointerAligned):
        (JSC::MachineStackMarker::markConservatively):
        * runtime/MachineStackMarker.h: Move the conservative marking code here.

        * runtime/MarkStack.h:
        (JSC::ConservativeSet::add):
        (JSC::ConservativeSet::mark): Changed to using a vector instead of hash
        set. Vector seems to be a bit faster, and it generates smaller code.

        * runtime/MarkedSpace.cpp:
        (JSC::MarkedSpace::containsSlowCase):
        * runtime/MarkedSpace.h:
        (JSC::MarkedSpace::isCellAligned):
        (JSC::MarkedSpace::isPossibleCell):
        (JSC::MarkedSpace::contains): Kept the code for determining whether a
        pointer pointed into marked space, and moved the code for marking
        a set of conservative pointers into the machine stack marker.

        * wtf/HashSet.h:
        (WTF::::add): Added two missing inlines that I noticed while testing
        vector vs hash set.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@76425 268f45cc-cd09-0410-ab3c-d52691b4dbfc