Currently the initial old generation size is set to the half of the
maximum old generation size. This is problematic for huge heaps.
This patch introduces an upper bound of 512MB (256MB) for x64 (x32).

Bug: chromium:961272
Change-Id: If4a6b839ebe688e5b0bc41749ac34f7a31849e21
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1605731
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61515}