Reviewed by Cameron Zwarich.

        Simplified Heap iteration
        https://bugs.webkit.org/show_bug.cgi?id=53393

        * runtime/CollectorHeapIterator.h:
        (JSC::CollectorHeapIterator::isValid):
        (JSC::CollectorHeapIterator::isLive):
        (JSC::CollectorHeapIterator::advance): Removed "max" argument to
        advance because it's a constant.
        (JSC::LiveObjectIterator::LiveObjectIterator):
        (JSC::LiveObjectIterator::operator++):
        (JSC::DeadObjectIterator::DeadObjectIterator):
        (JSC::DeadObjectIterator::operator++):
        (JSC::ObjectIterator::ObjectIterator):
        (JSC::ObjectIterator::operator++): Factored out common checks into
        two helper functions -- isValid() for "Am I past the end?" and isLive()
        for "Is the cell I'm pointing to live?".

        * runtime/MarkedSpace.cpp:
        (JSC::MarkedSpace::freeBlock):
        (JSC::MarkedSpace::sweep): Always sweep from the beginning of the heap
        to the end, to avoid making sweep subtly reliant on internal Heap state.
        (JSC::MarkedSpace::primaryHeapBegin):
        (JSC::MarkedSpace::primaryHeapEnd): Always be explicit about where
        iteration begins.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@77082 268f45cc-cd09-0410-ab3c-d52691b4dbfc