Reviewed by Adele.

    Reviewed by Adele.

        - fixed <rdar://problem/3746676> SAP WebDynpro app hangs inside JavaScript property map hash table code (deleted sentinel problem)

        * kjs/property_map.h: Added some private functions.
        * kjs/property_map.cpp:
        (KJS::PropertyMap::clear): Set sentinelCount to 0.
        (KJS::PropertyMap::put): Complete search for the element before choosing to use the deleted-element sentinel.
        Also keep sentinel count up to date when we destroy a sentinel by overwriting with a new added element.
        (KJS::PropertyMap::expand): Added. Calls rehash with a size 2x the old size, or 16.
        (KJS::PropertyMap::rehash): Added. Refactored the rehash code into a separate function.
        (KJS::PropertyMap::remove): Add one to sentinelCount, and rehash if 1/4 or more of the elements are
        deleted-element sentinels.
        (KJS::PropertyMap::checkConsistency): Check the sentinelCount.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@7281 268f45cc-cd09-0410-ab3c-d52691b4dbfc