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All thread checking code in Chromium should use the modern
THREAD_CHECKER API, which automatically gets removed when
!DCHECK_IS_ON().

BUG=

Change-Id: I70d3f12915445dc14be7f03c554c32c7fc12e2b2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1612377Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Robert Liao <robliao@chromium.org>
Auto-Submit: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660549}