Performance and stability improvements on all platforms.

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

Change-Id: Id1adaf424ed2c45cb7877bcd6842a6a777a5d27c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1617391
Reviewed-by: v8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/7.6.208@{#1}
Cr-Branched-From: 32cfe260375d6dc0303ffce8e2e3da790deac7c6-refs/heads/master@{#61615}