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There are strange behaviors observed in the field with the sampling
profiler. It seems there are two running sampling profiler but only
one is reporting events.

This CL is adding trace events to help investigate this problem.

R=wittman@chromium.org

Bug: 882982
Change-Id: I70925e841b8a1f0e47564350d142f056d8b8ae99
Reviewed-on: https://chromium-review.googlesource.com/c/1302318Reviewed-by: Mike Wittman <wittman@chromium.org>
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603235}