Revert "Remove layer-coverage-tracking experiment"

This reverts commit 688cb15faa641680346f7510bbf6e5d77053bc0e.

Reason for revert: Android roll & CK bots

Original change's description:
> Remove layer-coverage-tracking experiment
>
> This effectively reverts reviews.skia.org/122000
>
> Bug: skia:10987
> Change-Id: I989241110f17c0e3c2a896aea4bc2bc4cc8c910f
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/472801
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Brian Osman <brianosman@google.com>

Bug: skia:10987
Change-Id: Id2becfff07e4d9d72231939fb415a34ff9d96ed8
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/473140
Auto-Submit: Brian Osman <brianosman@google.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
10 files changed