Add a trace event when a task scheduler worker is active.

Example trace with this enabled: https://drive.google.com/file/d/11si1qvQUhRi1jMPNTzgJpqp3D-yFKOf7/view?usp=sharing

Also fix a racy setup order in MemoryDumpManagerTest exercised by this change.

R=fdoray@chromium.org

Bug: 811035
Change-Id: I328dca43f7b5bfd42bcf1a69b1e191fe41523ade
Reviewed-on: https://chromium-review.googlesource.com/913251
Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536177}
2 files changed