Make sure that the DummyScope top level scope used for pre-parsing have all members initialized. The type of this scope is set to global scope as it is a top level scope. Also ensure that the "naked" Scope constructor can only be used by sub-classes of Scope.

The bug of missing initiaalization of members in the DummyScope was found by Valgrind.
Review URL: http://codereview.chromium.org/173052

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2719 ce2b1a6d-e550-0410-aec6-3dcde31c8c00