Remove a DCHECK that got triggered in the rare condition that GC kicks in
during CompilationDependencies::Commit, changing the pretenuring decision,
thus leading to deoptimization. To make sure this rare case is properly
handled, add a new FLAG_pretenure_during_compilation and a cctest that
simulates it predictably.

R=jarin@chromium.org,mvstanton@chromium.org

Bug: v8:8520
Change-Id: If83f8a3d4659a694357b3869c931c7d7c164fd1a
Reviewed-on: https://chromium-review.googlesource.com/c/1363143
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58236}