Reviewed by Sam Weinig.

        Bug 21525: 55 StructureID leaks on Wikitravel's main page
        <https://bugs.webkit.org/show_bug.cgi?id=21525>

        Bug 21533: Simple JavaScript code leaks StructureIDs
        <https://bugs.webkit.org/show_bug.cgi?id=21533>

        StructureID::getEnumerablePropertyNames() ends up calling back to itself
        via JSObject::getPropertyNames(), which causes the PropertyNameArray to
        be cached twice. This leads to a memory leak in almost every use of
        JSObject::getPropertyNames() on an object. The fix here is based on a
        suggestion of Sam Weinig.

        This patch also fixes every StructureID leaks that occurs while running
        the Mozilla MemBuster test.

        * kjs/PropertyNameArray.h:
        (JSC::PropertyNameArray::PropertyNameArray):
        (JSC::PropertyNameArray::setCacheable):
        (JSC::PropertyNameArray::cacheable):
        * kjs/StructureID.cpp:
        (JSC::StructureID::getEnumerablePropertyNames):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@37508 268f45cc-cd09-0410-ab3c-d52691b4dbfc