Turn Runtime_MigrateInstance into Runtime_TryMigrateInstance

because it must not cause lazy deopts because it is called from deferred code that cannot handle lazy deopts.

Hat tip to Ben for doing most of the debugging work, and to Toon for writing the regression test.

BUG=chromium:315252
LOG=Y
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/131243003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18586 ce2b1a6d-e550-0410-aec6-3dcde31c8c00