Performance and stability improvements on all platforms.

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

Change-Id: Iab7dad7ff0cd7892a6e135498570778474d92e84
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1600981
Reviewed-by: v8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/7.6.123@{#1}
Cr-Branched-From: 2876c3f0d2b161cd8bc13f3e18d39d96a67784aa-refs/heads/master@{#61326}