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This allows reducing coupling and eliminating a circular include
in the Windows dependencies.

Rename updater_constants to constants.

Bug: 1054696
Change-Id: I4d6749c14191a9684ecdba364cb127a0a4af00a8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2068654
Commit-Queue: Sorin Jianu <sorin@chromium.org>
Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743728}