Performance and stability improvements on all platforms.

[email protected]

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I11c03e1966554bf2ee0434958b482ade24df98ab
Reviewed-on: https://chromium-review.googlesource.com/750642
Reviewed-by: v8 autoroll <[email protected]>
Cr-Commit-Position: refs/heads/6.4.186@{#1}
Cr-Branched-From: 781f7685b6b19a83414da248605b6af80e10e064-refs/heads/master@{#49068}