FCG implemented an optimziation which could avoid emitting a memento if the
memento was only needed for transitioning. This optimization is currently
turned off as we always run with pretenuring. Since this optimization will not
be ported to Ignition for now, we just remove the support from FCG.

Disabling allocation site pretenuring will then not make FCG and Iginition
diverge in their behavior.

BUG=chromium:693413

Change-Id: I69aea73426fc69d48e1fe6ed13caaf28f9cfb32f
Reviewed-on: https://chromium-review.googlesource.com/445258
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43345}