Make JSGlobalData per-thread.

        No change on SunSpider total.

        * wtf/ThreadSpecific.h: Re-enabled the actual implementation.

        * kjs/JSGlobalObject.cpp:
        (KJS::JSGlobalObject::~JSGlobalObject): Re-added a JSLock-related assertion. We'll probably
        want to preserve these somehow to keep legacy behavior in working condition.
        (KJS::JSGlobalObject::init): Initialize globalData pointer earlier, so that it is ready
        when updating JSGlobalObject linked list.

        * kjs/JSGlobalObject.h: (KJS::JSGlobalObject::head): Changed head() to be non-static, and
        to use JSGlobalData associated with the current object.

        * kjs/InitializeThreading.cpp: (KJS::initializeThreadingOnce): Removed a no longer needed
        Heap::registerAsMainThread() call.

        * kjs/JSGlobalData.h: Removed a lying lie comment - parserObjectExtraRefCounts is not
        transient, and while newParserObjects may conceptually be such, there is still some node
        manipulation going on outside Parser::parse which touches it.

        * kjs/JSGlobalData.cpp:
        (KJS::JSGlobalData::~JSGlobalData): Delete recently added members.
        (KJS::JSGlobalData::sharedInstance): Actually use a separate instance.

        * kjs/collector.cpp:
        (KJS::Heap::Heap):
        (KJS::Heap::~Heap): Added a destructor, which unconditionally deletes everything.
        (KJS::Heap::sweep): Removed code related to "collect on main thread only" logic.
        (KJS::Heap::collect): Ditto.
        (KJS::Heap::globalObjectCount): Explicitly use per-thread instance of JSGlobalObject linked
        list now that JSGlobalObject::head() is not static. Curently, WebCoreStatistics methods only
        work with the main thread currently anyway.
        (KJS::Heap::protectedGlobalObjectCount): Ditto.

        * kjs/collector.h: Removed code related to "collect on main thread only" logic.

        * JavaScriptCore.exp: Removed Heap::collectOnMainThreadOnly.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@34810 268f45cc-cd09-0410-ab3c-d52691b4dbfc