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Also moves some histogram codes to capture_mode_metrics.

Bug: 1140182
Test: added tests
Change-Id: I14fcb45512333ac3978884aae6db6a83cb1e8110
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2530220
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826938}