[status] Add alert for incremental cache liveness.
[status] Add alert for incremental cache liveness.

Bug: skia:7520
Change-Id: Ic371d2d2597375c19daa911a8702d65571bfd93e
Reviewed-on: https://skia-review.googlesource.com/98741
Reviewed-by: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>
Commit-Queue: Ben Wagner <3ef7217be91069877d94f7907ce5479000772cd3@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot