The flag configures both the young and old generation limits.

Bug: v8:9306
Change-Id: Ib94dcb6dc014864248a5926f585b54a83db28063
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1679500Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62440}