Replace sparse histogram with a linear one. This avoids extra lock on reporting.

Bug: 867488
Change-Id: If8b99bc2e5c4636ed42d5e68d9e08dc099e8bb27
Reviewed-on: https://chromium-review.googlesource.com/c/1277818
Reviewed-by: Peter Williamson <petewil@chromium.org>
Commit-Queue: Dmitry Titov <dimich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599031}
1 file changed