Performance and stability improvements on all platforms.

TBR=v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com

Change-Id: I9a94f13861ed18be72a5dfe4f20c9bda1be429fb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1578284
Reviewed-by: v8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/7.6.6@{#1}
Cr-Branched-From: 6957e23b5490d2fdf27aa60fade6fa488aca5de2-refs/heads/master@{#60943}