Performance and stability improvements on all platforms.

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

Change-Id: I34a977da836eba4893377ba2eefd53853696ca9b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1578286
Reviewed-by: v8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/7.6.8@{#1}
Cr-Branched-From: 49954eb56f81a94c4b32eeaedffcfaf7565efa7b-refs/heads/master@{#60954}