[Sheriff] Disabling SitePerProcessBrowserTest.VisibilityFrameDepthTest.

Flake portal shows it regularly flakes on Win10 and it has failed
on the Mac10.15 builder.

TBR=smcgruer@chromium.org

Bug: 1146083
Change-Id: Ic9caa365766bc4d3752eeebc95975ff4bb24cce5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2521350


Reviewed-by: Charlene Yan <cyan@chromium.org>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Charlene Yan <cyan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824557}