Add base::bits::AlignDown().

Like base::bits::Align(), but rounds down instead. Replace duplicate
implementations.

Change-Id: I7ad74d021feba26a34f2c80bc025e9ab9fe6660a
Reviewed-on: https://chromium-review.googlesource.com/c/1369047
Reviewed-by: vmpstr <[email protected]>
Reviewed-by: Dale Curtis <[email protected]>
Reviewed-by: Albert J. Wong <[email protected]>
Commit-Queue: Lei Zhang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#615610}
5 files changed