That is, change to use TimedHistogram (which functions properly on
background threads).

Bug: v8:6361
Change-Id: I821fb0afea97be422786778d576683f67667c31b
Reviewed-on: https://chromium-review.googlesource.com/559769
Commit-Queue: Karl Schimpf <kschimpf@chromium.org>
Reviewed-by: Brad Nelson <bradnelson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46529}