GitLab

Spring cleaning of V8 GC metrics

This removes some unused metrics and bumps expiration date of remaining
metrics to 2021-04-01.

Bug:1061974

Change-Id: Id5a7ec27e006b0ecaff56c8724982af660fd69b7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2130346Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#755958}