This patch enables ShouldOptimizeForMemoryUsage if the old generation
size is within 1/8th of the max old generation size.

This patch also passes the reduce-memory flag to incremental marking
whenever ShouldOptimizeForMemoryUsage is enabled.

Bug: chromium:824214
Change-Id: I5cfc0566ca0e23dfa1b8c0439a4e67424ddc852d
Reviewed-on: https://chromium-review.googlesource.com/973524
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52333}