Change allocations in test-heap to use handles. This makes the test

work when garbage collections are forced in random places.

Review URL: http://codereview.chromium.org/669153

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4033 ce2b1a6d-e550-0410-aec6-3dcde31c8c00