Declutter: Add histograms to track duplicate tabs

This will be helpful for determining declutter next steps, when it
comes to deduping tabs. Adds four histograms, for duplicate count
across all windows per profile, one for percentage of total tabs which
are duplicates across all windows per profile, and the same two but per
window.

Also adds a feature flag which is enabled by default, as a kill switch
if we run into performance issues.

Bug: 366294365
Change-Id: I4c1ad0452a97530040a9f8e35fc1fcd5a1becc01
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5879375
Reviewed-by: Dana Fried <dfried@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Commit-Queue: Emily Shack <emshack@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1359484}