coverage: add centipede coverage gathering code

The previous code wasn't working as intended. This should make things
work now.

Change-Id: If90cd7582692080dfb03851ad34fca697067a1cf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6425440
Auto-Submit: Paul Semel <paulsemel@chromium.org>
Commit-Queue: Ali Hijazi <ahijazi@chromium.org>
Commit-Queue: Paul Semel <paulsemel@chromium.org>
Reviewed-by: Ali Hijazi <ahijazi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1441441}
NOKEYCHECK=True
GitOrigin-RevId: cc17688f961d5b55c931c3144d789507f9da791a