Reviewed by Darin Adler.

        Variable-sized allocation (but still capped at 64 bytes)
        https://bugs.webkit.org/show_bug.cgi?id=55159
        
        SunSpider reports no change.

        * JavaScriptCore.exp: Some day, I hope not to have to edit this file.

        * runtime/Heap.cpp:
        (JSC::Heap::allocateSlowCase): Split allocation into a fast and slow
        case, so the fast case can inline size class selection and turn it into
        a compile-time constant.
        
        Changed the collect-on-every allocation debugging switch to collect only
        on every slow allocation, so you can still flip the switch without
        recompiling the world. This may also be preferable for debugging purposes,
        since collecting after every single allocation can be unusably slow,
        and can mask problems by running destructors early.

        * runtime/Heap.h: Ditto.

        * runtime/JSCell.h:
        (JSC::JSCell::MarkedSpace::sizeClassFor):
        (JSC::JSCell::Heap::allocate):
        (JSC::JSCell::JSCell::operator new): The inlining mentioned above.

        * runtime/MarkedBlock.h: Dropped the block size from 256KB to 16KB. With
        multiple size classes, allocating a full 256KB for the first allocation
        in a given class can be pathologically wasteful. (8KB, or 4KB Mac and
        8KB Windows, would be even better, but that seems to be a peformance
        regression for now.)
        
        * runtime/MarkedSpace.cpp:
        (JSC::MarkedSpace::MarkedSpace):
        (JSC::MarkedSpace::allocateBlock):
        (JSC::MarkedSpace::reset): There's more than one size class now, and its
        cell size is not constant.

        * runtime/MarkedSpace.h:
        (JSC::MarkedSpace::SizeClass::SizeClass): Ditto.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@79627 268f45cc-cd09-0410-ab3c-d52691b4dbfc