--verify-predictable mode added for ensuring that GC behaves deterministically.

--verify-predictable mode added for ensuring that GC behaves deterministically.
In order to be able to use it one should pass verifypredictable=on to the make tool or specify v8_enable_verify_predictable=1 in GYP_DEFINES.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/325553002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21892 ce2b1a6d-e550-0410-aec6-3dcde31c8c00