[code coverage] Mark shards with corrupted coverage data.

If a given shard has a profraw file that cannot be read, mark the shard
as invalid s.t. it can be retried.

R=martiniss,liaoyuke

Bug: 955012
Change-Id: I5b0b47d5ab55c9fd71c2ed09ff05b3c0831bf6b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1606762
Commit-Queue: Roberto Carrillo <robertocn@chromium.org>
Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Reviewed-by: Roberto Carrillo <robertocn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#667777}
3 files changed