I could not find a way to introduce simple yet useful assertions,
so I removed the assertions that broke tests.

The new patch just fixes the actual problem (GC triggered while raw pointers
are held in LookupResult).

Review URL: http://codereview.chromium.org/3030049

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5196 ce2b1a6d-e550-0410-aec6-3dcde31c8c00