Use Rotate*() functions instead of doing this manually.

Use Rotate*() functions instead of doing this manually.

Shouldn't make a difference in practice, but it's a bit more readable and it
gets the case of a 0 shift correct without undefined behavior.

BUG=463436
LOG=N

Review URL: https://codereview.chromium.org/975283002

Cr-Commit-Position: refs/heads/master@{#26975}