GitLab

Adds GUARDED_BY/EXCLUSIVE_LOCKS_REQUIRED annotations for the parts of
the sampling profiler implementation using locking.

Bug: 887645
Change-Id: Ibe96c541a50254af3822d6811fe03250543a98eb
Reviewed-on: https://chromium-review.googlesource.com/c/1283483Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Mike Wittman <wittman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600092}