JSClassRef is created context-free, but gets infatuated with the first context it sees.

        The implicit API contract is that JSClassRef can be used with any context on any thread.
        This no longer worked, because UStrings in the class were turned into per-context
        identifiers, and the cached JSObject prototype was tied to JSGlobalData, too.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@35293 268f45cc-cd09-0410-ab3c-d52691b4dbfc