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This incremental change adds the pref dependency and starts to register
feed preferences.

Bug: 831648
Change-Id: Ifb5ed97ac1de87a6319539839f9c57be46fb89b1
Reviewed-on: https://chromium-review.googlesource.com/1093982Reviewed-by: Filip Gorski <fgorski@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Commit-Queue: Sky Malice <skym@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567112}