Some tests and simplified TransitionArray copying

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

Committed: https://code.google.com/p/v8/source/detail?r=20710

[mvstanton, 2014-04-11 08:00:43]

Hi Toon,
Here is the test I was talking about, and I was able to simplify code in
TransitionArray::CopyInsert().

[Toon Verwaest, 2014-04-11 08:34:55]

lgtm

[mvstanton, 2014-04-14 08:58:12]

Committed patchset #1 manually as r20710 (presubmit successful).