No measurable change in test running time, we clean up only trivial
known things at disposal time and do not walk the heap, run real
finalizers, etc.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/135153007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19047 ce2b1a6d-e550-0410-aec6-3dcde31c8c00