Performance and stability improvements on all platforms.

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

Change-Id: I5b4873af1e89a1baa7353e21d06d9dfa7ec0c205
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1605349
Reviewed-by: v8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/7.6.143@{#1}
Cr-Branched-From: cc89f1e35b46144a7b0224d0714088a5598b6cac-refs/heads/master@{#61396}