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This is done by defining logging levels instead of just activating
complete hang watching per thread type. Hang watching a thread type can
be :

1) Deactivated.
2) Logging metrics to UMA only.
3) DumpWithoutCrashing on finding a hang.

Bug: 1135528
Change-Id: I98d04c24447129cd28e2d7d04ce26743e922fef3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2529192
Commit-Queue: Oliver Li <olivierli@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828506}