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This groups the prefs into actual user preferences vs internal/bookkeeping
ones, and updates some comments.

Bug: none
Change-Id: If3a9dc98ba4f6f26f76a69158fa839d281597d6f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1505442
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Auto-Submit: Marc Treib <treib@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638117}