Some tests and simplified TransitionArray copying

Tests for verifying that we deal correctly with shrinking transition
arrays while allocating a copy of one.

Also, we can rely on a transition array only shrinking and not
disappearing during gc while copying one.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/232883003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20710 ce2b1a6d-e550-0410-aec6-3dcde31c8c00